aboutsummaryrefslogtreecommitdiff
path: root/Documentation/fb/udlfb.rst
diff options
context:
space:
mode:
authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/fb/udlfb.rst
downloadlinux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz
linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip
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(). ...
Diffstat (limited to 'Documentation/fb/udlfb.rst')
-rw-r--r--Documentation/fb/udlfb.rst169
1 files changed, 169 insertions, 0 deletions
diff --git a/Documentation/fb/udlfb.rst b/Documentation/fb/udlfb.rst
new file mode 100644
index 000000000..99cfbb7a1
--- /dev/null
+++ b/Documentation/fb/udlfb.rst
@@ -0,0 +1,169 @@
+==============
+What is udlfb?
+==============
+
+This is a driver for DisplayLink USB 2.0 era graphics chips.
+
+DisplayLink chips provide simple hline/blit operations with some compression,
+pairing that with a hardware framebuffer (16MB) on the other end of the
+USB wire. That hardware framebuffer is able to drive the VGA, DVI, or HDMI
+monitor with no CPU involvement until a pixel has to change.
+
+The CPU or other local resource does all the rendering; optionally compares the
+result with a local shadow of the remote hardware framebuffer to identify
+the minimal set of pixels that have changed; and compresses and sends those
+pixels line-by-line via USB bulk transfers.
+
+Because of the efficiency of bulk transfers and a protocol on top that
+does not require any acks - the effect is very low latency that
+can support surprisingly high resolutions with good performance for
+non-gaming and non-video applications.
+
+Mode setting, EDID read, etc are other bulk or control transfers. Mode
+setting is very flexible - able to set nearly arbitrary modes from any timing.
+
+Advantages of USB graphics in general:
+
+ * Ability to add a nearly arbitrary number of displays to any USB 2.0
+ capable system. On Linux, number of displays is limited by fbdev interface
+ (FB_MAX is currently 32). Of course, all USB devices on the same
+ host controller share the same 480Mbs USB 2.0 interface.
+
+Advantages of supporting DisplayLink chips with kernel framebuffer interface:
+
+ * The actual hardware functionality of DisplayLink chips matches nearly
+ one-to-one with the fbdev interface, making the driver quite small and
+ tight relative to the functionality it provides.
+ * X servers and other applications can use the standard fbdev interface
+ from user mode to talk to the device, without needing to know anything
+ about USB or DisplayLink's protocol at all. A "displaylink" X driver
+ and a slightly modified "fbdev" X driver are among those that already do.
+
+Disadvantages:
+
+ * Fbdev's mmap interface assumes a real hardware framebuffer is mapped.
+ In the case of USB graphics, it is just an allocated (virtual) buffer.
+ Writes need to be detected and encoded into USB bulk transfers by the CPU.
+ Accurate damage/changed area notifications work around this problem.
+ In the future, hopefully fbdev will be enhanced with an small standard
+ interface to allow mmap clients to report damage, for the benefit
+ of virtual or remote framebuffers.
+ * Fbdev does not arbitrate client ownership of the framebuffer well.
+ * Fbcon assumes the first framebuffer it finds should be consumed for console.
+ * It's not clear what the future of fbdev is, given the rise of KMS/DRM.
+
+How to use it?
+==============
+
+Udlfb, when loaded as a module, will match against all USB 2.0 generation
+DisplayLink chips (Alex and Ollie family). It will then attempt to read the EDID
+of the monitor, and set the best common mode between the DisplayLink device
+and the monitor's capabilities.
+
+If the DisplayLink device is successful, it will paint a "green screen" which
+means that from a hardware and fbdev software perspective, everything is good.
+
+At that point, a /dev/fb? interface will be present for user-mode applications
+to open and begin writing to the framebuffer of the DisplayLink device using
+standard fbdev calls. Note that if mmap() is used, by default the user mode
+application must send down damage notifications to trigger repaints of the
+changed regions. Alternatively, udlfb can be recompiled with experimental
+defio support enabled, to support a page-fault based detection mechanism
+that can work without explicit notification.
+
+The most common client of udlfb is xf86-video-displaylink or a modified
+xf86-video-fbdev X server. These servers have no real DisplayLink specific
+code. They write to the standard framebuffer interface and rely on udlfb
+to do its thing. The one extra feature they have is the ability to report
+rectangles from the X DAMAGE protocol extension down to udlfb via udlfb's
+damage interface (which will hopefully be standardized for all virtual
+framebuffers that need damage info). These damage notifications allow
+udlfb to efficiently process the changed pixels.
+
+Module Options
+==============
+
+Special configuration for udlfb is usually unnecessary. There are a few
+options, however.
+
+From the command line, pass options to modprobe::
+
+ modprobe udlfb fb_defio=0 console=1 shadow=1
+
+Or change options on the fly by editing
+/sys/module/udlfb/parameters/PARAMETER_NAME ::
+
+ cd /sys/module/udlfb/parameters
+ ls # to see a list of parameter names
+ sudo nano PARAMETER_NAME
+ # change the parameter in place, and save the file.
+
+Unplug/replug USB device to apply with new settings.
+
+Or to apply options permanently, create a modprobe configuration file
+like /etc/modprobe.d/udlfb.conf with text::
+
+ options udlfb fb_defio=0 console=1 shadow=1
+
+Accepted boolean options:
+
+=============== ================================================================
+fb_defio Make use of the fb_defio (CONFIG_FB_DEFERRED_IO) kernel
+ module to track changed areas of the framebuffer by page faults.
+ Standard fbdev applications that use mmap but that do not
+ report damage, should be able to work with this enabled.
+ Disable when running with X server that supports reporting
+ changed regions via ioctl, as this method is simpler,
+ more stable, and higher performance.
+ default: fb_defio=1
+
+console Allow fbcon to attach to udlfb provided framebuffers.
+ Can be disabled if fbcon and other clients
+ (e.g. X with --shared-vt) are in conflict.
+ default: console=1
+
+shadow Allocate a 2nd framebuffer to shadow what's currently across
+ the USB bus in device memory. If any pixels are unchanged,
+ do not transmit. Spends host memory to save USB transfers.
+ Enabled by default. Only disable on very low memory systems.
+ default: shadow=1
+=============== ================================================================
+
+Sysfs Attributes
+================
+
+Udlfb creates several files in /sys/class/graphics/fb?
+Where ? is the sequential framebuffer id of the particular DisplayLink device
+
+======================== ========================================================
+edid If a valid EDID blob is written to this file (typically
+ by a udev rule), then udlfb will use this EDID as a
+ backup in case reading the actual EDID of the monitor
+ attached to the DisplayLink device fails. This is
+ especially useful for fixed panels, etc. that cannot
+ communicate their capabilities via EDID. Reading
+ this file returns the current EDID of the attached
+ monitor (or last backup value written). This is
+ useful to get the EDID of the attached monitor,
+ which can be passed to utilities like parse-edid.
+
+metrics_bytes_rendered 32-bit count of pixel bytes rendered
+
+metrics_bytes_identical 32-bit count of how many of those bytes were found to be
+ unchanged, based on a shadow framebuffer check
+
+metrics_bytes_sent 32-bit count of how many bytes were transferred over
+ USB to communicate the resulting changed pixels to the
+ hardware. Includes compression and protocol overhead
+
+metrics_cpu_kcycles_used 32-bit count of CPU cycles used in processing the
+ above pixels (in thousands of cycles).
+
+metrics_reset Write-only. Any write to this file resets all metrics
+ above to zero. Note that the 32-bit counters above
+ roll over very quickly. To get reliable results, design
+ performance tests to start and finish in a very short
+ period of time (one minute or less is safe).
+======================== ========================================================
+
+Bernie Thompson <bernie@plugable.com>