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author | 2023-02-21 18:24:12 -0800 | |
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committer | 2023-02-21 18:24:12 -0800 | |
commit | 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch) | |
tree | cc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/fb/udlfb.rst | |
download | linux-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.rst | 169 |
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> |