From 106b4a2a78b2a2f14885604891957b84bba502db Mon Sep 17 00:00:00 2001 From: Adrian Betschart Date: Fri, 11 Sep 2026 17:13:14 +0200 Subject: drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validation amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and uses the first encoding that validates. YCbCr 4:4:4 is listed before RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the "color format" property is left at AUTO, even though RGB fits the same link. That contradicts the documented AUTO behaviour for HDMI in enum drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when the bandwidth is not available or the mode is 4:2:0-only), which the amdgpu implementation of the property also describes. It also leaves the "Broadcast RGB" property without effect on such sinks, since the quantization range it selects only applies to RGB output. Try RGB first. The mask still holds every encoding the sink supports, so a mode that cannot carry RGB falls back exactly as before. For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI sink that advertised it. Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation") Suggested-by: Adolfo Rodrigues Assisted-by: Claude Code:claude-fable-5-1 Signed-off-by: Adrian Betschart Reviewed-by: Fangzhi Zuo Tested-by: Adolfo Rodrigues Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher (cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7) --- Documentation/input/ff.rst | 265 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 265 insertions(+) create mode 100644 Documentation/input/ff.rst (limited to 'Documentation/input/ff.rst') diff --git a/Documentation/input/ff.rst b/Documentation/input/ff.rst new file mode 100644 index 000000000..5a1da42c3 --- /dev/null +++ b/Documentation/input/ff.rst @@ -0,0 +1,265 @@ +======================== +Force feedback for Linux +======================== + +:Author: Johann Deneux on 2001/04/22. +:Updated: Anssi Hannula on 2006/04/09. + +You may redistribute this file. Please remember to include shape.svg and +interactive.svg as well. + +Introduction +~~~~~~~~~~~~ + +This document describes how to use force feedback devices under Linux. The +goal is not to support these devices as if they were simple input-only devices +(as it is already the case), but to really enable the rendering of force +effects. +This document only describes the force feedback part of the Linux input +interface. Please read joydev/joystick.rst and input.rst before reading further +this document. + +Instructions to the user +~~~~~~~~~~~~~~~~~~~~~~~~ + +To enable force feedback, you have to: + +1. have your kernel configured with evdev and a driver that supports your + device. +2. make sure evdev module is loaded and /dev/input/event* device files are + created. + +Before you start, let me WARN you that some devices shake violently during the +initialisation phase. This happens for example with my "AVB Top Shot Pegasus". +To stop this annoying behaviour, move your joystick to its limits. Anyway, you +should keep a hand on your device, in order to avoid it to break down if +something goes wrong. + +If you have a serial iforce device, you need to start inputattach. See +joydev/joystick.rst for details. + +Does it work ? +-------------- + +There is an utility called fftest that will allow you to test the driver:: + + % fftest /dev/input/eventXX + +Instructions to the developer +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +All interactions are done using the event API. That is, you can use ioctl() +and write() on /dev/input/eventXX. +This information is subject to change. + +Querying device capabilities +---------------------------- + +:: + + #include + #include + + #define BITS_TO_LONGS(x) \ + (((x) + 8 * sizeof (unsigned long) - 1) / (8 * sizeof (unsigned long))) + unsigned long features[BITS_TO_LONGS(FF_CNT)]; + int ioctl(int file_descriptor, int request, unsigned long *features); + +"request" must be EVIOCGBIT(EV_FF, size of features array in bytes ) + +Returns the features supported by the device. features is a bitfield with the +following bits: + +- FF_CONSTANT can render constant force effects +- FF_PERIODIC can render periodic effects with the following waveforms: + + - FF_SQUARE square waveform + - FF_TRIANGLE triangle waveform + - FF_SINE sine waveform + - FF_SAW_UP sawtooth up waveform + - FF_SAW_DOWN sawtooth down waveform + - FF_CUSTOM custom waveform + +- FF_RAMP can render ramp effects +- FF_SPRING can simulate the presence of a spring +- FF_FRICTION can simulate friction +- FF_DAMPER can simulate damper effects +- FF_RUMBLE rumble effects +- FF_INERTIA can simulate inertia +- FF_GAIN gain is adjustable +- FF_AUTOCENTER autocenter is adjustable + +.. note:: + + - In most cases you should use FF_PERIODIC instead of FF_RUMBLE. All + devices that support FF_RUMBLE support FF_PERIODIC (square, triangle, + sine) and the other way around. + + - The exact syntax FF_CUSTOM is undefined for the time being as no driver + supports it yet. + +:: + + int ioctl(int fd, EVIOCGEFFECTS, int *n); + +Returns the number of effects the device can keep in its memory. + +Uploading effects to the device +------------------------------- + +:: + + #include + #include + + int ioctl(int file_descriptor, int request, struct ff_effect *effect); + +"request" must be EVIOCSFF. + +"effect" points to a structure describing the effect to upload. The effect is +uploaded, but not played. +The content of effect may be modified. In particular, its field "id" is set +to the unique id assigned by the driver. This data is required for performing +some operations (removing an effect, controlling the playback). +The "id" field must be set to -1 by the user in order to tell the driver to +allocate a new effect. + +Effects are file descriptor specific. + +See for a description of the ff_effect struct. You +should also find help in a few sketches, contained in files shape.svg +and interactive.svg: + +.. kernel-figure:: shape.svg + + Shape + +.. kernel-figure:: interactive.svg + + Interactive + + +Removing an effect from the device +---------------------------------- + +:: + + int ioctl(int fd, EVIOCRMFF, effect.id); + +This makes room for new effects in the device's memory. Note that this also +stops the effect if it was playing. + +Controlling the playback of effects +----------------------------------- + +Control of playing is done with write(). Below is an example: + +:: + + #include + #include + + struct input_event play; + struct input_event stop; + struct ff_effect effect; + int fd; + ... + fd = open("/dev/input/eventXX", O_RDWR); + ... + /* Play three times */ + play.type = EV_FF; + play.code = effect.id; + play.value = 3; + + write(fd, (const void*) &play, sizeof(play)); + ... + /* Stop an effect */ + stop.type = EV_FF; + stop.code = effect.id; + stop.value = 0; + + write(fd, (const void*) &stop, sizeof(stop)); + +Setting the gain +---------------- + +Not all devices have the same strength. Therefore, users should set a gain +factor depending on how strong they want effects to be. This setting is +persistent across access to the driver. + +:: + + /* Set the gain of the device + int gain; /* between 0 and 100 */ + struct input_event ie; /* structure used to communicate with the driver */ + + ie.type = EV_FF; + ie.code = FF_GAIN; + ie.value = 0xFFFFUL * gain / 100; + + if (write(fd, &ie, sizeof(ie)) == -1) + perror("set gain"); + +Enabling/Disabling autocenter +----------------------------- + +The autocenter feature quite disturbs the rendering of effects in my opinion, +and I think it should be an effect, which computation depends on the game +type. But you can enable it if you want. + +:: + + int autocenter; /* between 0 and 100 */ + struct input_event ie; + + ie.type = EV_FF; + ie.code = FF_AUTOCENTER; + ie.value = 0xFFFFUL * autocenter / 100; + + if (write(fd, &ie, sizeof(ie)) == -1) + perror("set auto-center"); + +A value of 0 means "no auto-center". + +Dynamic update of an effect +--------------------------- + +Proceed as if you wanted to upload a new effect, except that instead of +setting the id field to -1, you set it to the wanted effect id. +Normally, the effect is not stopped and restarted. However, depending on the +type of device, not all parameters can be dynamically updated. For example, +the direction of an effect cannot be updated with iforce devices. In this +case, the driver stops the effect, up-load it, and restart it. + +Therefore it is recommended to dynamically change direction while the effect +is playing only when it is ok to restart the effect with a replay count of 1. + +Information about the status of effects +--------------------------------------- + +Every time the status of an effect is changed, an event is sent. The values +and meanings of the fields of the event are as follows:: + + struct input_event { + /* When the status of the effect changed */ + struct timeval time; + + /* Set to EV_FF_STATUS */ + unsigned short type; + + /* Contains the id of the effect */ + unsigned short code; + + /* Indicates the status */ + unsigned int value; + }; + + FF_STATUS_STOPPED The effect stopped playing + FF_STATUS_PLAYING The effect started to play + +.. note:: + + - Status feedback is only supported by iforce driver. If you have + a really good reason to use this, please contact + linux-joystick@atrey.karlin.mff.cuni.cz or anssi.hannula@gmail.com + so that support for it can be added to the rest of the drivers. -- cgit v1.3.1