kernel/linux.git/drivers/gpu/drm/mgag200, branch v6.12.80

drm/mgag200: fix mgag200_bmc_stop_scanout()

2026-02-11T12:40:27+00:00

[ Upstream commit 0e0c8f4d16de92520623aa1ea485cadbf64e6929 ] The mgag200_bmc_stop_scanout() function is called by the .atomic_disable() handler for the MGA G200 VGA BMC encoder. This function performs a few register writes to inform the BMC of an upcoming mode change, and then polls to wait until the BMC actually stops. The polling is implemented using a busy loop with udelay() and an iteration timeout of 300, resulting in the function blocking for 300 milliseconds. The function gets called ultimately by the output_poll_execute work thread for the DRM output change polling thread of the mgag200 driver: kworker/0:0-mm_ 3528 [000] 4555.315364: ffffffffaa0e25b3 delay_halt.part.0+0x33 ffffffffc03f6188 mgag200_bmc_stop_scanout+0x178 ffffffffc087ae7a disable_outputs+0x12a ffffffffc087c12a drm_atomic_helper_commit_tail+0x1a ffffffffc03fa7b6 mgag200_mode_config_helper_atomic_commit_tail+0x26 ffffffffc087c9c1 commit_tail+0x91 ffffffffc087d51b drm_atomic_helper_commit+0x11b ffffffffc0509694 drm_atomic_commit+0xa4 ffffffffc05105e8 drm_client_modeset_commit_atomic+0x1e8 ffffffffc0510ce6 drm_client_modeset_commit_locked+0x56 ffffffffc0510e24 drm_client_modeset_commit+0x24 ffffffffc088a743 __drm_fb_helper_restore_fbdev_mode_unlocked+0x93 ffffffffc088a683 drm_fb_helper_hotplug_event+0xe3 ffffffffc050f8aa drm_client_dev_hotplug+0x9a ffffffffc088555a output_poll_execute+0x29a ffffffffa9b35924 process_one_work+0x194 ffffffffa9b364ee worker_thread+0x2fe ffffffffa9b3ecad kthread+0xdd ffffffffa9a08549 ret_from_fork+0x29 On a server running ptp4l with the mgag200 driver loaded, we found that ptp4l would sometimes get blocked from execution because of this busy waiting loop. Every so often, approximately once every 20 minutes -- though with large variance -- the output_poll_execute() thread would detect some sort of change that required performing a hotplug event which results in attempting to stop the BMC scanout, resulting in a 300msec delay on one CPU. On this system, ptp4l was pinned to a single CPU. When the output_poll_execute() thread ran on that CPU, it blocked ptp4l from executing for its 300 millisecond duration. This resulted in PTP service disruptions such as failure to send a SYNC message on time, failure to handle ANNOUNCE messages on time, and clock check warnings from the application. All of this despite the application being configured with FIFO_RT and a higher priority than the background workqueue tasks. (However, note that the kernel did not use CONFIG_PREEMPT...) It is unclear if the event is due to a faulty VGA connection, another bug, or actual events causing a change in the connection. At least on the system under test it is not a one-time event and consistently causes disruption to the time sensitive applications. The function has some helpful comments explaining what steps it is attempting to take. In particular, step 3a and 3b are explained as such: 3a - The third step is to verify if there is an active scan. We are waiting on a 0 on remhsyncsts (. 3b - This step occurs only if the remove is actually scanning. We are waiting for the end of the frame which is a 1 on remvsyncsts (). The actual steps 3a and 3b are implemented as while loops with a non-sleeping udelay(). The first step iterates while the tmp value at position 0 is *not* set. That is, it keeps iterating as long as the bit is zero. If the bit is already 0 (because there is no active scan), it will iterate the entire 300 attempts which wastes 300 milliseconds in total. This is opposite of what the description claims. The step 3b logic only executes if we do not iterate over the entire 300 attempts in the first loop. If it does trigger, it is trying to check and wait for a 1 on the remvsyncsts. However, again the condition is actually inverted and it will loop as long as the bit is 1, stopping once it hits zero (rather than the explained attempt to wait until we see a 1). Worse, both loops are implemented using non-sleeping waits which spin instead of allowing the scheduler to run other processes. If the kernel is not configured to allow arbitrary preemption, it will waste valuable CPU time doing nothing. There does not appear to be any documentation for the BMC register interface, beyond what is in the comments here. It seems more probable that the comment here is correct and the implementation accidentally got inverted from the intended logic. Reading through other DRM driver implementations, it does not appear that the .atomic_enable or .atomic_disable handlers need to delay instead of sleep. For example, the ast_astdp_encoder_helper_atomic_disable() function calls ast_dp_set_phy_sleep() which uses msleep(). The "atomic" in the name is referring to the atomic modesetting support, which is the support to enable atomic configuration from userspace, and not to the "atomic context" of the kernel. There is no reason to use udelay() here if a sleep would be sufficient. Replace the while loops with a read_poll_timeout() based implementation that will sleep between iterations, and which stops polling once the condition is met (instead of looping as long as the condition is met). This aligns with the commented behavior and avoids blocking on the CPU while doing nothing. Note the RREG_DAC is implemented using a statement expression to allow working properly with the read_poll_timeout family of functions. The other RREG_ macros ought to be cleaned up to have better semantics, and several places in the mgag200 driver could make use of RREG_DAC or similar RREG_* macros should likely be cleaned up for better semantics as well, but that task has been left as a future cleanup for a non-bugfix. Fixes: 414c45310625 ("mgag200: initial g200se driver (v2)") Suggested-by: Thomas Zimmermann Signed-off-by: Jacob Keller Reviewed-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Signed-off-by: Thomas Zimmermann Link: https://patch.msgid.link/20260202-jk-mgag200-fix-bad-udelay-v2-1-ce1e9665987d@intel.com Signed-off-by: Sasha Levin

drm/mgag200: Fix big-endian support

2026-01-08T09:14:54+00:00

commit 6cb31fba137d45e682ce455b8ea364f44d5d4f98 upstream. Unlike the original, deleted Matrox mga driver, the new mgag200 driver has the XRGB frame-buffer byte swapped on big-endian "RISC" systems. Fix by enabling byte swapping "PowerPC" OPMODE for any __BIG_ENDIAN config. Fixes: 414c45310625 ("mgag200: initial g200se driver (v2)") Signed-off-by: René Rebe Cc: stable@kernel.org Reviewed-by: Thomas Zimmermann Signed-off-by: Thomas Zimmermann Link: https://patch.msgid.link/20251208.141827.965103015954471168.rene@exactco.de Signed-off-by: Greg Kroah-Hartman

drm/mgag200: Fix value in register

2025-04-25T08:48:03+00:00

commit 76c332d119f9048c6e16b52359f401510f18b2ff upstream. Fix an off-by-one error when setting the vblanking start in . Commit d6460bd52c27 ("drm/mgag200: Add dedicated variables for blanking fields") switched the value from crtc_vdisplay to crtc_vblank_start, which DRM helpers copy from the former. The commit missed to subtract one though. Reported-by: Wakko Warner Closes: https://lore.kernel.org/dri-devel/CAMwc25rKPKooaSp85zDq2eh-9q4UPZD=RqSDBRp1fAagDnmRmA@mail.gmail.com/ Reported-by: Сергей Closes: https://lore.kernel.org/all/5b193b75-40b1-4342-a16a-ae9fc62f245a@gmail.com/ Closes: https://bbs.archlinux.org/viewtopic.php?id=303819 Signed-off-by: Thomas Zimmermann Fixes: d6460bd52c27 ("drm/mgag200: Add dedicated variables for blanking fields") Cc: Thomas Zimmermann Cc: Jocelyn Falempe Cc: Dave Airlie Cc: dri-devel@lists.freedesktop.org Cc: # v6.12+ Reviewed-by: Jocelyn Falempe Tested-by: Wakko Warner Link: https://lore.kernel.org/r/20250416083847.51764-1-tzimmermann@suse.de Signed-off-by: Greg Kroah-Hartman

Revert "drm/mgag200: Add vblank support"

2024-10-17T06:49:45+00:00

This reverts commit 6c9e14ee9f519ee605a3694fbfa4711284781d22. This reverts commit d5070c9b29440c270b534bbacd636b8fa558e82b. This reverts commit 89c6ea2006e2d39b125848fb0195c08fa0b354be. The VLINE interrupt doesn't work correctly on G200SE-A (at least). We have also seen missing interrupts on G200ER. So revert vblank support. Fixes frozen displays and warnings about missed vblanks. [ 33.818362] [CRTC:34:crtc-0] vblank wait timed out From the vblank code, the driver only keeps the register constants and the line that disables all interrupts in mgag200_device_init(). Both is still useful without vblank handling. Reported-by: Tony Luck Closes: https://lore.kernel.org/dri-devel/Zvx6lSi7oq5xvTZb@agluck-desk3.sc.intel.com/raw Tested-by: Tony Luck Signed-off-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20241015063932.8620-1-tzimmermann@suse.de

drm/mgag200: Remove BMC output

2024-08-09T06:13:48+00:00

Mgag200's BMC connector tracks the status of an underlying physical connector and updates the BMC status accordingly. This functionality works around GNOME's settings app, which cannot handle multiple outputs on the same CRTC. The workaround is now obsolete as the VGA-BMC connector handles BMC support internally. Hence, remove the driver's code and the BMC output entirely. Signed-off-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20240805130622.63458-6-tzimmermann@suse.de

drm/mgag200: vga-bmc: Control BMC scanout from encoder

2024-08-09T06:13:47+00:00

Move calls to stop and start BMC scanout from CRTC helpers to the VGA-BMC encoder's atomic_disable and atomic_enable. Makes the BMC scanout transparent to the CRTC. DRM's atomic helpers call an encoder's atomic_disable and atomic_enable helpers for all enabled encoders. The BMC stops scanning out the VGA signal if modeset disables the VGA encoder, and starts scanning out if the modeset enables the VGA encoder. Signed-off-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20240805130622.63458-5-tzimmermann@suse.de

drm/mgag200: vga-bmc: Control CRTC VIDRST flag from encoder

2024-08-09T06:13:47+00:00

Control the VIDRST pin from the VGA-BMC encoder's atomic_check and remove the respective code from CRTC. Makes the VIDRST functionality fully composable. The VIDRST pin allows an external clock source to control the SYNC signals of the Matrox chip. The functionality is part of the CRTC, but depends on the presence of the clock source. This is the case for some BMCs, so control the pin from the VGA-BMC output. Signed-off-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20240805130622.63458-4-tzimmermann@suse.de

drm/mgag200: vga-bmc: Transparently handle BMC

2024-08-09T06:13:46+00:00

The VGA-BMC connector selects the VGA output if a display has been attached to the physical connector. Otherwise it selects the BMC output. In any case, the connector status is set to 'detected', so that the userspace compositor displays to it. Depending on the setting, the connector's display modes either come from the VGA monitor's EDID or from an internal list of BMC-compatible modes. Signed-off-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20240805130622.63458-3-tzimmermann@suse.de

drm/mgag200: Add VGA-BMC output

2024-08-09T06:13:45+00:00

Duplicate VGA output to VGA-BMC output and update all code for Matrox server chips. The new output represents a VGA output that has a BMC attached to it. No functional changes so far. Signed-off-by: Thomas Zimmermann Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20240805130622.63458-2-tzimmermann@suse.de

drm/mgag200: Fix VBLANK interrupt handling

2024-08-01T06:33:24+00:00

Fix support for VBLANK interrupts on G200ER, G200EV and G200SE, which use a slightly different implementation than the others. The original commits forgot to update the custom helpers when adding interrupt handling for VBLANK events. Signed-off-by: Thomas Zimmermann Fixes: 89c6ea2006e2 ("drm/mgag200: Add vblank support") Fixes: d5070c9b2944 ("drm/mgag200: Implement struct drm_crtc_funcs.get_vblank_timestamp") Cc: Thomas Zimmermann Cc: Jocelyn Falempe Cc: Gerd Hoffmann Cc: Sam Ravnborg Cc: Dave Airlie Cc: dri-devel@lists.freedesktop.org Acked-by: Sui Jingfeng Reviewed-by: Jocelyn Falempe Link: https://patchwork.freedesktop.org/patch/msgid/20240731071004.519566-1-tzimmermann@suse.de