Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted

Pull networking updates from Jakub Kicinski:
 "Core:

   - Add dedicated kmem_cache for typical/small skb->head, avoid having
     to access struct page at kfree time, and improve memory use.

   - Introduce sysctl to set default RPS configuration for new netdevs.

   - Define Netlink protocol specification format which can be used to
     describe messages used by each family and auto-generate parsers.
     Add tools for generating kernel data structures and uAPI headers.

   - Expose all net/core sysctls inside netns.

   - Remove 4s sleep in netpoll if carrier is instantly detected on
     boot.

   - Add configurable limit of MDB entries per port, and port-vlan.

   - Continue populating drop reasons throughout the stack.

   - Retire a handful of legacy Qdiscs and classifiers.

  Protocols:

   - Support IPv4 big TCP (TSO frames larger than 64kB).

   - Add IP_LOCAL_PORT_RANGE socket option, to control local port range
     on socket by socket basis.

   - Track and report in procfs number of MPTCP sockets used.

   - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path
     manager.

   - IPv6: don't check net.ipv6.route.max_size and rely on garbage
     collection to free memory (similarly to IPv4).

   - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986).

   - ICMP: add per-rate limit counters.

   - Add support for user scanning requests in ieee802154.

   - Remove static WEP support.

   - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate
     reporting.

   - WiFi 7 EHT channel puncturing support (client & AP).

  BPF:

   - Add a rbtree data structure following the "next-gen data structure"
     precedent set by recently added linked list, that is, by using
     kfunc + kptr instead of adding a new BPF map type.

   - Expose XDP hints via kfuncs with initial support for RX hash and
     timestamp metadata.

   - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to
     better support decap on GRE tunnel devices not operating in collect
     metadata.

   - Improve x86 JIT's codegen for PROBE_MEM runtime error checks.

   - Remove the need for trace_printk_lock for bpf_trace_printk and
     bpf_trace_vprintk helpers.

   - Extend libbpf's bpf_tracing.h support for tracing arguments of
     kprobes/uprobes and syscall as a special case.

   - Significantly reduce the search time for module symbols by
     livepatch and BPF.

   - Enable cpumasks to be used as kptrs, which is useful for tracing
     programs tracking which tasks end up running on which CPUs in
     different time intervals.

   - Add support for BPF trampoline on s390x and riscv64.

   - Add capability to export the XDP features supported by the NIC.

   - Add __bpf_kfunc tag for marking kernel functions as kfuncs.

   - Add cgroup.memory=nobpf kernel parameter option to disable BPF
     memory accounting for container environments.

  Netfilter:

   - Remove the CLUSTERIP target. It has been marked as obsolete for
     years, and we still have WARN splats wrt races of the out-of-band
     /proc interface installed by this target.

   - Add 'destroy' commands to nf_tables. They are identical to the
     existing 'delete' commands, but do not return an error if the
     referenced object (set, chain, rule...) did not exist.

  Driver API:

   - Improve cpumask_local_spread() locality to help NICs set the right
     IRQ affinity on AMD platforms.

   - Separate C22 and C45 MDIO bus transactions more clearly.

   - Introduce new DCB table to control DSCP rewrite on egress.

   - Support configuration of Physical Layer Collision Avoidance (PLCA)
     Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of
     shared medium Ethernet.

   - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing
     preemption of low priority frames by high priority frames.

   - Add support for controlling MACSec offload using netlink SET.

   - Rework devlink instance refcounts to allow registration and
     de-registration under the instance lock. Split the code into
     multiple files, drop some of the unnecessarily granular locks and
     factor out common parts of netlink operation handling.

   - Add TX frame aggregation parameters (for USB drivers).

   - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning
     messages with notifications for debug.

   - Allow offloading of UDP NEW connections via act_ct.

   - Add support for per action HW stats in TC.

   - Support hardware miss to TC action (continue processing in SW from
     a specific point in the action chain).

   - Warn if old Wireless Extension user space interface is used with
     modern cfg80211/mac80211 drivers. Do not support Wireless
     Extensions for Wi-Fi 7 devices at all. Everyone should switch to
     using nl80211 interface instead.

   - Improve the CAN bit timing configuration. Use extack to return
     error messages directly to user space, update the SJW handling,
     including the definition of a new default value that will benefit
     CAN-FD controllers, by increasing their oscillator tolerance.

  New hardware / drivers:

   - Ethernet:
      - nVidia BlueField-3 support (control traffic driver)
      - Ethernet support for imx93 SoCs
      - Motorcomm yt8531 gigabit Ethernet PHY
      - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA)
      - Microchip LAN8841 PHY (incl. cable diagnostics and PTP)
      - Amlogic gxl MDIO mux

   - WiFi:
      - RealTek RTL8188EU (rtl8xxxu)
      - Qualcomm Wi-Fi 7 devices (ath12k)

   - CAN:
      - Renesas R-Car V4H

  Drivers:

   - Bluetooth:
      - Set Per Platform Antenna Gain (PPAG) for Intel controllers.

   - Ethernet NICs:
      - Intel (1G, igc):
         - support TSN / Qbv / packet scheduling features of i226 model
      - Intel (100G, ice):
         - use GNSS subsystem instead of TTY
         - multi-buffer XDP support
         - extend support for GPIO pins to E823 devices
      - nVidia/Mellanox:
         - update the shared buffer configuration on PFC commands
         - implement PTP adjphase function for HW offset control
         - TC support for Geneve and GRE with VF tunnel offload
         - more efficient crypto key management method
         - multi-port eswitch support
      - Netronome/Corigine:
         - add DCB IEEE support
         - support IPsec offloading for NFP3800
      - Freescale/NXP (enetc):
         - support XDP_REDIRECT for XDP non-linear buffers
         - improve reconfig, avoid link flap and waiting for idle
         - support MAC Merge layer
      - Other NICs:
         - sfc/ef100: add basic devlink support for ef100
         - ionic: rx_push mode operation (writing descriptors via MMIO)
         - bnxt: use the auxiliary bus abstraction for RDMA
         - r8169: disable ASPM and reset bus in case of tx timeout
         - cpsw: support QSGMII mode for J721e CPSW9G
         - cpts: support pulse-per-second output
         - ngbe: add an mdio bus driver
         - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing
         - r8152: handle devices with FW with NCM support
         - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation
         - virtio-net: support multi buffer XDP
         - virtio/vsock: replace virtio_vsock_pkt with sk_buff
         - tsnep: XDP support

   - Ethernet high-speed switches:
      - nVidia/Mellanox (mlxsw):
         - add support for latency TLV (in FW control messages)
      - Microchip (sparx5):
         - separate explicit and implicit traffic forwarding rules, make
           the implicit rules always active
         - add support for egress DSCP rewrite
         - IS0 VCAP support (Ingress Classification)
         - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS
           etc.)
         - ES2 VCAP support (Egress Access Control)
         - support for Per-Stream Filtering and Policing (802.1Q,
           8.6.5.1)

   - Ethernet embedded switches:
      - Marvell (mv88e6xxx):
         - add MAB (port auth) offload support
         - enable PTP receive for mv88e6390
      - NXP (ocelot):
         - support MAC Merge layer
         - support for the the vsc7512 internal copper phys
      - Microchip:
         - lan9303: convert to PHYLINK
         - lan966x: support TC flower filter statistics
         - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x
         - lan937x: support Credit Based Shaper configuration
         - ksz9477: support Energy Efficient Ethernet
      - other:
         - qca8k: convert to regmap read/write API, use bulk operations
         - rswitch: Improve TX timestamp accuracy

   - Intel WiFi (iwlwifi):
      - EHT (Wi-Fi 7) rate reporting
      - STEP equalizer support: transfer some STEP (connection to radio
        on platforms with integrated wifi) related parameters from the
        BIOS to the firmware.

   - Qualcomm 802.11ax WiFi (ath11k):
      - IPQ5018 support
      - Fine Timing Measurement (FTM) responder role support
      - channel 177 support

   - MediaTek WiFi (mt76):
      - per-PHY LED support
      - mt7996: EHT (Wi-Fi 7) support
      - Wireless Ethernet Dispatch (WED) reset support
      - switch to using page pool allocator

   - RealTek WiFi (rtw89):
      - support new version of Bluetooth co-existance

   - Mobile:
      - rmnet: support TX aggregation"

* tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits)
  page_pool: add a comment explaining the fragment counter usage
  net: ethtool: fix __ethtool_dev_mm_supported() implementation
  ethtool: pse-pd: Fix double word in comments
  xsk: add linux/vmalloc.h to xsk.c
  sefltests: netdevsim: wait for devlink instance after netns removal
  selftest: fib_tests: Always cleanup before exit
  net/mlx5e: Align IPsec ASO result memory to be as required by hardware
  net/mlx5e: TC, Set CT miss to the specific ct action instance
  net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
  net/mlx5: Refactor tc miss handling to a single function
  net/mlx5: Kconfig: Make tc offload depend on tc skb extension
  net/sched: flower: Support hardware miss to tc action
  net/sched: flower: Move filter handle initialization earlier
  net/sched: cls_api: Support hardware miss to tc action
  net/sched: Rename user cookie and act cookie
  sfc: fix builds without CONFIG_RTC_LIB
  sfc: clean up some inconsistent indentings
  net/mlx4_en: Introduce flexible array to silence overflow warning
  net: lan966x: Fix possible deadlock inside PTP
  net/ulp: Remove redundant ->clone() test in inet_clone_ulp().
  ...

1 files changed, 818 insertions, 0 deletions

diff --git a/drivers/tty/ehv_bytechan.c b/drivers/tty/ehv_bytechan.c
new file mode 100644
index 000000000..8595483f4
--- /dev/null
+++ b/drivers/tty/ehv_bytechan.c
@@ -0,0 +1,818 @@
+// SPDX-License-Identifier: GPL-2.0
+/* ePAPR hypervisor byte channel device driver
+ *
+ * Copyright 2009-2011 Freescale Semiconductor, Inc.
+ *
+ * Author: Timur Tabi <timur@freescale.com>
+ *
+ * This driver support three distinct interfaces, all of which are related to
+ * ePAPR hypervisor byte channels.
+ *
+ * 1) An early-console (udbg) driver.  This provides early console output
+ * through a byte channel.  The byte channel handle must be specified in a
+ * Kconfig option.
+ *
+ * 2) A normal console driver.  Output is sent to the byte channel designated
+ * for stdout in the device tree.  The console driver is for handling kernel
+ * printk calls.
+ *
+ * 3) A tty driver, which is used to handle user-space input and output.  The
+ * byte channel used for the console is designated as the default tty.
+ */
+
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/interrupt.h>
+#include <linux/fs.h>
+#include <linux/poll.h>
+#include <asm/epapr_hcalls.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/cdev.h>
+#include <linux/console.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/circ_buf.h>
+#include <asm/udbg.h>
+
+/* The size of the transmit circular buffer.  This must be a power of two. */
+#define BUF_SIZE	2048
+
+/* Per-byte channel private data */
+struct ehv_bc_data {
+	struct device *dev;
+	struct tty_port port;
+	uint32_t handle;
+	unsigned int rx_irq;
+	unsigned int tx_irq;
+
+	spinlock_t lock;	/* lock for transmit buffer */
+	unsigned char buf[BUF_SIZE];	/* transmit circular buffer */
+	unsigned int head;	/* circular buffer head */
+	unsigned int tail;	/* circular buffer tail */
+
+	int tx_irq_enabled;	/* true == TX interrupt is enabled */
+};
+
+/* Array of byte channel objects */
+static struct ehv_bc_data *bcs;
+
+/* Byte channel handle for stdout (and stdin), taken from device tree */
+static unsigned int stdout_bc;
+
+/* Virtual IRQ for the byte channel handle for stdin, taken from device tree */
+static unsigned int stdout_irq;
+
+/**************************** SUPPORT FUNCTIONS ****************************/
+
+/*
+ * Enable the transmit interrupt
+ *
+ * Unlike a serial device, byte channels have no mechanism for disabling their
+ * own receive or transmit interrupts.  To emulate that feature, we toggle
+ * the IRQ in the kernel.
+ *
+ * We cannot just blindly call enable_irq() or disable_irq(), because these
+ * calls are reference counted.  This means that we cannot call enable_irq()
+ * if interrupts are already enabled.  This can happen in two situations:
+ *
+ * 1. The tty layer makes two back-to-back calls to ehv_bc_tty_write()
+ * 2. A transmit interrupt occurs while executing ehv_bc_tx_dequeue()
+ *
+ * To work around this, we keep a flag to tell us if the IRQ is enabled or not.
+ */
+static void enable_tx_interrupt(struct ehv_bc_data *bc)
+{
+	if (!bc->tx_irq_enabled) {
+		enable_irq(bc->tx_irq);
+		bc->tx_irq_enabled = 1;
+	}
+}
+
+static void disable_tx_interrupt(struct ehv_bc_data *bc)
+{
+	if (bc->tx_irq_enabled) {
+		disable_irq_nosync(bc->tx_irq);
+		bc->tx_irq_enabled = 0;
+	}
+}
+
+/*
+ * find the byte channel handle to use for the console
+ *
+ * The byte channel to be used for the console is specified via a "stdout"
+ * property in the /chosen node.
+ */
+static int find_console_handle(void)
+{
+	struct device_node *np = of_stdout;
+	const uint32_t *iprop;
+
+	/* We don't care what the aliased node is actually called.  We only
+	 * care if it's compatible with "epapr,hv-byte-channel", because that
+	 * indicates that it's a byte channel node.
+	 */
+	if (!np || !of_device_is_compatible(np, "epapr,hv-byte-channel"))
+		return 0;
+
+	stdout_irq = irq_of_parse_and_map(np, 0);
+	if (!stdout_irq) {
+		pr_err("ehv-bc: no 'interrupts' property in %pOF node\n", np);
+		return 0;
+	}
+
+	/*
+	 * The 'hv-handle' property contains the handle for this byte channel.
+	 */
+	iprop = of_get_property(np, "hv-handle", NULL);
+	if (!iprop) {
+		pr_err("ehv-bc: no 'hv-handle' property in %pOFn node\n",
+		       np);
+		return 0;
+	}
+	stdout_bc = be32_to_cpu(*iprop);
+	return 1;
+}
+
+static unsigned int local_ev_byte_channel_send(unsigned int handle,
+					       unsigned int *count,
+					       const char *p)
+{
+	char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
+	unsigned int c = *count;
+
+	if (c < sizeof(buffer)) {
+		memcpy(buffer, p, c);
+		memset(&buffer[c], 0, sizeof(buffer) - c);
+		p = buffer;
+	}
+	return ev_byte_channel_send(handle, count, p);
+}
+
+/*************************** EARLY CONSOLE DRIVER ***************************/
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
+
+/*
+ * send a byte to a byte channel, wait if necessary
+ *
+ * This function sends a byte to a byte channel, and it waits and
+ * retries if the byte channel is full.  It returns if the character
+ * has been sent, or if some error has occurred.
+ *
+ */
+static void byte_channel_spin_send(const char data)
+{
+	int ret, count;
+
+	do {
+		count = 1;
+		ret = local_ev_byte_channel_send(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
+					   &count, &data);
+	} while (ret == EV_EAGAIN);
+}
+
+/*
+ * The udbg subsystem calls this function to display a single character.
+ * We convert CR to a CR/LF.
+ */
+static void ehv_bc_udbg_putc(char c)
+{
+	if (c == '\n')
+		byte_channel_spin_send('\r');
+
+	byte_channel_spin_send(c);
+}
+
+/*
+ * early console initialization
+ *
+ * PowerPC kernels support an early printk console, also known as udbg.
+ * This function must be called via the ppc_md.init_early function pointer.
+ * At this point, the device tree has been unflattened, so we can obtain the
+ * byte channel handle for stdout.
+ *
+ * We only support displaying of characters (putc).  We do not support
+ * keyboard input.
+ */
+void __init udbg_init_ehv_bc(void)
+{
+	unsigned int rx_count, tx_count;
+	unsigned int ret;
+
+	/* Verify the byte channel handle */
+	ret = ev_byte_channel_poll(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
+				   &rx_count, &tx_count);
+	if (ret)
+		return;
+
+	udbg_putc = ehv_bc_udbg_putc;
+	register_early_udbg_console();
+
+	udbg_printf("ehv-bc: early console using byte channel handle %u\n",
+		    CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
+}
+
+#endif
+
+/****************************** CONSOLE DRIVER ******************************/
+
+static struct tty_driver *ehv_bc_driver;
+
+/*
+ * Byte channel console sending worker function.
+ *
+ * For consoles, if the output buffer is full, we should just spin until it
+ * clears.
+ */
+static int ehv_bc_console_byte_channel_send(unsigned int handle, const char *s,
+			     unsigned int count)
+{
+	unsigned int len;
+	int ret = 0;
+
+	while (count) {
+		len = min_t(unsigned int, count, EV_BYTE_CHANNEL_MAX_BYTES);
+		do {
+			ret = local_ev_byte_channel_send(handle, &len, s);
+		} while (ret == EV_EAGAIN);
+		count -= len;
+		s += len;
+	}
+
+	return ret;
+}
+
+/*
+ * write a string to the console
+ *
+ * This function gets called to write a string from the kernel, typically from
+ * a printk().  This function spins until all data is written.
+ *
+ * We copy the data to a temporary buffer because we need to insert a \r in
+ * front of every \n.  It's more efficient to copy the data to the buffer than
+ * it is to make multiple hcalls for each character or each newline.
+ */
+static void ehv_bc_console_write(struct console *co, const char *s,
+				 unsigned int count)
+{
+	char s2[EV_BYTE_CHANNEL_MAX_BYTES];
+	unsigned int i, j = 0;
+	char c;
+
+	for (i = 0; i < count; i++) {
+		c = *s++;
+
+		if (c == '\n')
+			s2[j++] = '\r';
+
+		s2[j++] = c;
+		if (j >= (EV_BYTE_CHANNEL_MAX_BYTES - 1)) {
+			if (ehv_bc_console_byte_channel_send(stdout_bc, s2, j))
+				return;
+			j = 0;
+		}
+	}
+
+	if (j)
+		ehv_bc_console_byte_channel_send(stdout_bc, s2, j);
+}
+
+/*
+ * When /dev/console is opened, the kernel iterates the console list looking
+ * for one with ->device and then calls that method. On success, it expects
+ * the passed-in int* to contain the minor number to use.
+ */
+static struct tty_driver *ehv_bc_console_device(struct console *co, int *index)
+{
+	*index = co->index;
+
+	return ehv_bc_driver;
+}
+
+static struct console ehv_bc_console = {
+	.name		= "ttyEHV",
+	.write		= ehv_bc_console_write,
+	.device		= ehv_bc_console_device,
+	.flags		= CON_PRINTBUFFER | CON_ENABLED,
+};
+
+/*
+ * Console initialization
+ *
+ * This is the first function that is called after the device tree is
+ * available, so here is where we determine the byte channel handle and IRQ for
+ * stdout/stdin, even though that information is used by the tty and character
+ * drivers.
+ */
+static int __init ehv_bc_console_init(void)
+{
+	if (!find_console_handle()) {
+		pr_debug("ehv-bc: stdout is not a byte channel\n");
+		return -ENODEV;
+	}
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
+	/* Print a friendly warning if the user chose the wrong byte channel
+	 * handle for udbg.
+	 */
+	if (stdout_bc != CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE)
+		pr_warn("ehv-bc: udbg handle %u is not the stdout handle\n",
+			CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
+#endif
+
+	/* add_preferred_console() must be called before register_console(),
+	   otherwise it won't work.  However, we don't want to enumerate all the
+	   byte channels here, either, since we only care about one. */
+
+	add_preferred_console(ehv_bc_console.name, ehv_bc_console.index, NULL);
+	register_console(&ehv_bc_console);
+
+	pr_info("ehv-bc: registered console driver for byte channel %u\n",
+		stdout_bc);
+
+	return 0;
+}
+console_initcall(ehv_bc_console_init);
+
+/******************************** TTY DRIVER ********************************/
+
+/*
+ * byte channel receive interrupt handler
+ *
+ * This ISR is called whenever data is available on a byte channel.
+ */
+static irqreturn_t ehv_bc_tty_rx_isr(int irq, void *data)
+{
+	struct ehv_bc_data *bc = data;
+	unsigned int rx_count, tx_count, len;
+	int count;
+	char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
+	int ret;
+
+	/* Find out how much data needs to be read, and then ask the TTY layer
+	 * if it can handle that much.  We want to ensure that every byte we
+	 * read from the byte channel will be accepted by the TTY layer.
+	 */
+	ev_byte_channel_poll(bc->handle, &rx_count, &tx_count);
+	count = tty_buffer_request_room(&bc->port, rx_count);
+
+	/* 'count' is the maximum amount of data the TTY layer can accept at
+	 * this time.  However, during testing, I was never able to get 'count'
+	 * to be less than 'rx_count'.  I'm not sure whether I'm calling it
+	 * correctly.
+	 */
+
+	while (count > 0) {
+		len = min_t(unsigned int, count, sizeof(buffer));
+
+		/* Read some data from the byte channel.  This function will
+		 * never return more than EV_BYTE_CHANNEL_MAX_BYTES bytes.
+		 */
+		ev_byte_channel_receive(bc->handle, &len, buffer);
+
+		/* 'len' is now the amount of data that's been received. 'len'
+		 * can't be zero, and most likely it's equal to one.
+		 */
+
+		/* Pass the received data to the tty layer. */
+		ret = tty_insert_flip_string(&bc->port, buffer, len);
+
+		/* 'ret' is the number of bytes that the TTY layer accepted.
+		 * If it's not equal to 'len', then it means the buffer is
+		 * full, which should never happen.  If it does happen, we can
+		 * exit gracefully, but we drop the last 'len - ret' characters
+		 * that we read from the byte channel.
+		 */
+		if (ret != len)
+			break;
+
+		count -= len;
+	}
+
+	/* Tell the tty layer that we're done. */
+	tty_flip_buffer_push(&bc->port);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * dequeue the transmit buffer to the hypervisor
+ *
+ * This function, which can be called in interrupt context, dequeues as much
+ * data as possible from the transmit buffer to the byte channel.
+ */
+static void ehv_bc_tx_dequeue(struct ehv_bc_data *bc)
+{
+	unsigned int count;
+	unsigned int len, ret;
+	unsigned long flags;
+
+	do {
+		spin_lock_irqsave(&bc->lock, flags);
+		len = min_t(unsigned int,
+			    CIRC_CNT_TO_END(bc->head, bc->tail, BUF_SIZE),
+			    EV_BYTE_CHANNEL_MAX_BYTES);
+
+		ret = local_ev_byte_channel_send(bc->handle, &len, bc->buf + bc->tail);
+
+		/* 'len' is valid only if the return code is 0 or EV_EAGAIN */
+		if (!ret || (ret == EV_EAGAIN))
+			bc->tail = (bc->tail + len) & (BUF_SIZE - 1);
+
+		count = CIRC_CNT(bc->head, bc->tail, BUF_SIZE);
+		spin_unlock_irqrestore(&bc->lock, flags);
+	} while (count && !ret);
+
+	spin_lock_irqsave(&bc->lock, flags);
+	if (CIRC_CNT(bc->head, bc->tail, BUF_SIZE))
+		/*
+		 * If we haven't emptied the buffer, then enable the TX IRQ.
+		 * We'll get an interrupt when there's more room in the
+		 * hypervisor's output buffer.
+		 */
+		enable_tx_interrupt(bc);
+	else
+		disable_tx_interrupt(bc);
+	spin_unlock_irqrestore(&bc->lock, flags);
+}
+
+/*
+ * byte channel transmit interrupt handler
+ *
+ * This ISR is called whenever space becomes available for transmitting
+ * characters on a byte channel.
+ */
+static irqreturn_t ehv_bc_tty_tx_isr(int irq, void *data)
+{
+	struct ehv_bc_data *bc = data;
+
+	ehv_bc_tx_dequeue(bc);
+	tty_port_tty_wakeup(&bc->port);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * This function is called when the tty layer has data for us send.  We store
+ * the data first in a circular buffer, and then dequeue as much of that data
+ * as possible.
+ *
+ * We don't need to worry about whether there is enough room in the buffer for
+ * all the data.  The purpose of ehv_bc_tty_write_room() is to tell the tty
+ * layer how much data it can safely send to us.  We guarantee that
+ * ehv_bc_tty_write_room() will never lie, so the tty layer will never send us
+ * too much data.
+ */
+static int ehv_bc_tty_write(struct tty_struct *ttys, const unsigned char *s,
+			    int count)
+{
+	struct ehv_bc_data *bc = ttys->driver_data;
+	unsigned long flags;
+	unsigned int len;
+	unsigned int written = 0;
+
+	while (1) {
+		spin_lock_irqsave(&bc->lock, flags);
+		len = CIRC_SPACE_TO_END(bc->head, bc->tail, BUF_SIZE);
+		if (count < len)
+			len = count;
+		if (len) {
+			memcpy(bc->buf + bc->head, s, len);
+			bc->head = (bc->head + len) & (BUF_SIZE - 1);
+		}
+		spin_unlock_irqrestore(&bc->lock, flags);
+		if (!len)
+			break;
+
+		s += len;
+		count -= len;
+		written += len;
+	}
+
+	ehv_bc_tx_dequeue(bc);
+
+	return written;
+}
+
+/*
+ * This function can be called multiple times for a given tty_struct, which is
+ * why we initialize bc->ttys in ehv_bc_tty_port_activate() instead.
+ *
+ * The tty layer will still call this function even if the device was not
+ * registered (i.e. tty_register_device() was not called).  This happens
+ * because tty_register_device() is optional and some legacy drivers don't
+ * use it.  So we need to check for that.
+ */
+static int ehv_bc_tty_open(struct tty_struct *ttys, struct file *filp)
+{
+	struct ehv_bc_data *bc = &bcs[ttys->index];
+
+	if (!bc->dev)
+		return -ENODEV;
+
+	return tty_port_open(&bc->port, ttys, filp);
+}
+
+/*
+ * Amazingly, if ehv_bc_tty_open() returns an error code, the tty layer will
+ * still call this function to close the tty device.  So we can't assume that
+ * the tty port has been initialized.
+ */
+static void ehv_bc_tty_close(struct tty_struct *ttys, struct file *filp)
+{
+	struct ehv_bc_data *bc = &bcs[ttys->index];
+
+	if (bc->dev)
+		tty_port_close(&bc->port, ttys, filp);
+}
+
+/*
+ * Return the amount of space in the output buffer
+ *
+ * This is actually a contract between the driver and the tty layer outlining
+ * how much write room the driver can guarantee will be sent OR BUFFERED.  This
+ * driver MUST honor the return value.
+ */
+static unsigned int ehv_bc_tty_write_room(struct tty_struct *ttys)
+{
+	struct ehv_bc_data *bc = ttys->driver_data;
+	unsigned long flags;
+	unsigned int count;
+
+	spin_lock_irqsave(&bc->lock, flags);
+	count = CIRC_SPACE(bc->head, bc->tail, BUF_SIZE);
+	spin_unlock_irqrestore(&bc->lock, flags);
+
+	return count;
+}
+
+/*
+ * Stop sending data to the tty layer
+ *
+ * This function is called when the tty layer's input buffers are getting full,
+ * so the driver should stop sending it data.  The easiest way to do this is to
+ * disable the RX IRQ, which will prevent ehv_bc_tty_rx_isr() from being
+ * called.
+ *
+ * The hypervisor will continue to queue up any incoming data.  If there is any
+ * data in the queue when the RX interrupt is enabled, we'll immediately get an
+ * RX interrupt.
+ */
+static void ehv_bc_tty_throttle(struct tty_struct *ttys)
+{
+	struct ehv_bc_data *bc = ttys->driver_data;
+
+	disable_irq(bc->rx_irq);
+}
+
+/*
+ * Resume sending data to the tty layer
+ *
+ * This function is called after previously calling ehv_bc_tty_throttle().  The
+ * tty layer's input buffers now have more room, so the driver can resume
+ * sending it data.
+ */
+static void ehv_bc_tty_unthrottle(struct tty_struct *ttys)
+{
+	struct ehv_bc_data *bc = ttys->driver_data;
+
+	/* If there is any data in the queue when the RX interrupt is enabled,
+	 * we'll immediately get an RX interrupt.
+	 */
+	enable_irq(bc->rx_irq);
+}
+
+static void ehv_bc_tty_hangup(struct tty_struct *ttys)
+{
+	struct ehv_bc_data *bc = ttys->driver_data;
+
+	ehv_bc_tx_dequeue(bc);
+	tty_port_hangup(&bc->port);
+}
+
+/*
+ * TTY driver operations
+ *
+ * If we could ask the hypervisor how much data is still in the TX buffer, or
+ * at least how big the TX buffers are, then we could implement the
+ * .wait_until_sent and .chars_in_buffer functions.
+ */
+static const struct tty_operations ehv_bc_ops = {
+	.open		= ehv_bc_tty_open,
+	.close		= ehv_bc_tty_close,
+	.write		= ehv_bc_tty_write,
+	.write_room	= ehv_bc_tty_write_room,
+	.throttle	= ehv_bc_tty_throttle,
+	.unthrottle	= ehv_bc_tty_unthrottle,
+	.hangup		= ehv_bc_tty_hangup,
+};
+
+/*
+ * initialize the TTY port
+ *
+ * This function will only be called once, no matter how many times
+ * ehv_bc_tty_open() is called.  That's why we register the ISR here, and also
+ * why we initialize tty_struct-related variables here.
+ */
+static int ehv_bc_tty_port_activate(struct tty_port *port,
+				    struct tty_struct *ttys)
+{
+	struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
+	int ret;
+
+	ttys->driver_data = bc;
+
+	ret = request_irq(bc->rx_irq, ehv_bc_tty_rx_isr, 0, "ehv-bc", bc);
+	if (ret < 0) {
+		dev_err(bc->dev, "could not request rx irq %u (ret=%i)\n",
+		       bc->rx_irq, ret);
+		return ret;
+	}
+
+	/* request_irq also enables the IRQ */
+	bc->tx_irq_enabled = 1;
+
+	ret = request_irq(bc->tx_irq, ehv_bc_tty_tx_isr, 0, "ehv-bc", bc);
+	if (ret < 0) {
+		dev_err(bc->dev, "could not request tx irq %u (ret=%i)\n",
+		       bc->tx_irq, ret);
+		free_irq(bc->rx_irq, bc);
+		return ret;
+	}
+
+	/* The TX IRQ is enabled only when we can't write all the data to the
+	 * byte channel at once, so by default it's disabled.
+	 */
+	disable_tx_interrupt(bc);
+
+	return 0;
+}
+
+static void ehv_bc_tty_port_shutdown(struct tty_port *port)
+{
+	struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
+
+	free_irq(bc->tx_irq, bc);
+	free_irq(bc->rx_irq, bc);
+}
+
+static const struct tty_port_operations ehv_bc_tty_port_ops = {
+	.activate = ehv_bc_tty_port_activate,
+	.shutdown = ehv_bc_tty_port_shutdown,
+};
+
+static int ehv_bc_tty_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct ehv_bc_data *bc;
+	const uint32_t *iprop;
+	unsigned int handle;
+	int ret;
+	static unsigned int index = 1;
+	unsigned int i;
+
+	iprop = of_get_property(np, "hv-handle", NULL);
+	if (!iprop) {
+		dev_err(&pdev->dev, "no 'hv-handle' property in %pOFn node\n",
+			np);
+		return -ENODEV;
+	}
+
+	/* We already told the console layer that the index for the console
+	 * device is zero, so we need to make sure that we use that index when
+	 * we probe the console byte channel node.
+	 */
+	handle = be32_to_cpu(*iprop);
+	i = (handle == stdout_bc) ? 0 : index++;
+	bc = &bcs[i];
+
+	bc->handle = handle;
+	bc->head = 0;
+	bc->tail = 0;
+	spin_lock_init(&bc->lock);
+
+	bc->rx_irq = irq_of_parse_and_map(np, 0);
+	bc->tx_irq = irq_of_parse_and_map(np, 1);
+	if (!bc->rx_irq || !bc->tx_irq) {
+		dev_err(&pdev->dev, "no 'interrupts' property in %pOFn node\n",
+			np);
+		ret = -ENODEV;
+		goto error;
+	}
+
+	tty_port_init(&bc->port);
+	bc->port.ops = &ehv_bc_tty_port_ops;
+
+	bc->dev = tty_port_register_device(&bc->port, ehv_bc_driver, i,
+			&pdev->dev);
+	if (IS_ERR(bc->dev)) {
+		ret = PTR_ERR(bc->dev);
+		dev_err(&pdev->dev, "could not register tty (ret=%i)\n", ret);
+		goto error;
+	}
+
+	dev_set_drvdata(&pdev->dev, bc);
+
+	dev_info(&pdev->dev, "registered /dev/%s%u for byte channel %u\n",
+		ehv_bc_driver->name, i, bc->handle);
+
+	return 0;
+
+error:
+	tty_port_destroy(&bc->port);
+	irq_dispose_mapping(bc->tx_irq);
+	irq_dispose_mapping(bc->rx_irq);
+
+	memset(bc, 0, sizeof(struct ehv_bc_data));
+	return ret;
+}
+
+static const struct of_device_id ehv_bc_tty_of_ids[] = {
+	{ .compatible = "epapr,hv-byte-channel" },
+	{}
+};
+
+static struct platform_driver ehv_bc_tty_driver = {
+	.driver = {
+		.name = "ehv-bc",
+		.of_match_table = ehv_bc_tty_of_ids,
+		.suppress_bind_attrs = true,
+	},
+	.probe		= ehv_bc_tty_probe,
+};
+
+/**
+ * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
+ *
+ * This function is called when this driver is loaded.
+ */
+static int __init ehv_bc_init(void)
+{
+	struct tty_driver *driver;
+	struct device_node *np;
+	unsigned int count = 0; /* Number of elements in bcs[] */
+	int ret;
+
+	pr_info("ePAPR hypervisor byte channel driver\n");
+
+	/* Count the number of byte channels */
+	for_each_compatible_node(np, NULL, "epapr,hv-byte-channel")
+		count++;
+
+	if (!count)
+		return -ENODEV;
+
+	/* The array index of an element in bcs[] is the same as the tty index
+	 * for that element.  If you know the address of an element in the
+	 * array, then you can use pointer math (e.g. "bc - bcs") to get its
+	 * tty index.
+	 */
+	bcs = kcalloc(count, sizeof(struct ehv_bc_data), GFP_KERNEL);
+	if (!bcs)
+		return -ENOMEM;
+
+	driver = tty_alloc_driver(count, TTY_DRIVER_REAL_RAW |
+			TTY_DRIVER_DYNAMIC_DEV);
+	if (IS_ERR(driver)) {
+		ret = PTR_ERR(driver);
+		goto err_free_bcs;
+	}
+
+	driver->driver_name = "ehv-bc";
+	driver->name = ehv_bc_console.name;
+	driver->type = TTY_DRIVER_TYPE_CONSOLE;
+	driver->subtype = SYSTEM_TYPE_CONSOLE;
+	driver->init_termios = tty_std_termios;
+	tty_set_operations(driver, &ehv_bc_ops);
+
+	ret = tty_register_driver(driver);
+	if (ret) {
+		pr_err("ehv-bc: could not register tty driver (ret=%i)\n", ret);
+		goto err_tty_driver_kref_put;
+	}
+
+	ehv_bc_driver = driver;
+
+	ret = platform_driver_register(&ehv_bc_tty_driver);
+	if (ret) {
+		pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
+		       ret);
+		goto err_deregister_tty_driver;
+	}
+
+	return 0;
+
+err_deregister_tty_driver:
+	ehv_bc_driver = NULL;
+	tty_unregister_driver(driver);
+err_tty_driver_kref_put:
+	tty_driver_kref_put(driver);
+err_free_bcs:
+	kfree(bcs);
+
+	return ret;
+}
+device_initcall(ehv_bc_init);