Hi Am 10.07.23 um 11:52 schrieb Javier Martinez Canillas:
Thomas Zimmermann <tzimmermann@xxxxxxx> writes: Hello Thomas,Generate a hotplug event after registering a client to allow the client to configure its display. Remove the hotplug calls from the existing clients for fbdev emulation. This change fixes a concurrency bug between registering a client and receiving events from the DRM core. The bug is present in the fbdev emulation of all drivers. The fbdev emulation currently generates a hotplug event before registering the client to the device. For each new output, the DRM core sends an additional hotplug event to each registered client. If the DRM core detects first output between sending the artificial hotplug and registering the device, the output's hotplug event gets lost. If this is the first output, the fbdev console display remains dark. This has been observed with amdgpu and fbdev-generic. Fix this by adding hotplug generation directly to the client's register helper drm_client_register(). Registering the client and receiving events are serialized by struct drm_device.clientlist_mutex. So an output is either configured by the initial hotplug event, or the client has already been registered. The bug was originally added in commit 6e3f17ee73f7 ("drm/fb-helper: generic: Call drm_client_add() after setup is done"), in which adding a client and receiving a hotplug event switched order. It was hidden, as most hardware and drivers have at least on static output configured. Other drivers didn't use the internal DRM client or still had struct drm_mode_config_funcs.output_poll_changed set. That callback handled hotplug events as well. After not setting the callback in amdgpu in commit 0e3172bac3f4 ("drm/amdgpu: Don't set struct drm_driver.output_poll_changed"), amdgpu did not show a framebuffer console if output events got lost. The bug got copy-pasted from fbdev-generic into the other fbdev emulation. Reported-by: Moritz Duge <MoritzDuge@xxxxxxxxxxxx> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/2649Aren't you missing a Fixes: for 0e3172bac3f4 too? Since that's the commit that unmasked the bug for amdgpu, IMO that is the most important to list.
Well, OK.
Fixes: 6e3f17ee73f7 ("drm/fb-helper: generic: Call drm_client_add() after setup is done") Fixes: 8ab59da26bc0 ("drm/fb-helper: Move generic fbdev emulation into separate source file") Fixes: b79fe9abd58b ("drm/fbdev-dma: Implement fbdev emulation for GEM DMA helpers") Fixes: 63c381552f69 ("drm/armada: Implement fbdev emulation as in-kernel client") Fixes: 49953b70e7d3 ("drm/exynos: Implement fbdev emulation as in-kernel client") Fixes: 8f1aaccb04b7 ("drm/gma500: Implement client-based fbdev emulation") Fixes: 940b869c2f2f ("drm/msm: Implement fbdev emulation as in-kernel client") Fixes: 9e69bcd88e45 ("drm/omapdrm: Implement fbdev emulation as in-kernel client") Fixes: e317a69fe891 ("drm/radeon: Implement client-based fbdev emulation") Fixes: 71ec16f45ef8 ("drm/tegra: Implement fbdev emulation as in-kernel client") Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx> Tested-by: Moritz Duge <MoritzDuge@xxxxxxxxxxxx> Tested-by: Torsten Krah <krah.tm@xxxxxxxxx> Tested-by: Paul Schyska <pschyska@xxxxxxxxx> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> Cc: David Airlie <airlied@xxxxxxxxx> Cc: Noralf Trønnes <noralf@xxxxxxxxxxx> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> Cc: Maxime Ripard <mripard@xxxxxxxxxx> Cc: Javier Martinez Canillas <javierm@xxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Inki Dae <inki.dae@xxxxxxxxxxx> Cc: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> Cc: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> Cc: Patrik Jakobsson <patrik.r.jakobsson@xxxxxxxxx> Cc: Rob Clark <robdclark@xxxxxxxxx> Cc: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> Cc: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> Cc: Alex Deucher <alexander.deucher@xxxxxxx> Cc: "Christian König" <christian.koenig@xxxxxxx> Cc: "Pan, Xinhui" <Xinhui.Pan@xxxxxxx> Cc: Thierry Reding <thierry.reding@xxxxxxxxx> Cc: Mikko Perttunen <mperttunen@xxxxxxxxxx> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx Cc: linux-samsung-soc@xxxxxxxxxxxxxxx Cc: linux-arm-msm@xxxxxxxxxxxxxxx Cc: freedreno@xxxxxxxxxxxxxxxxxxxxx Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx Cc: linux-tegra@xxxxxxxxxxxxxxx Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> # v5.2+While it's true that the but was introduced by commit 6e3f17ee73f7 and that landed in v5.2, I wonder if this patch could even be applied to such olders Linux versions. Probably in practice it would be at most backported to v6.2, which is the release that exposed the bug for the amdgpu driver.
No idea. The fix looks simple enough, but a lot has changed in the surrounding code.
Best regards Thomas
Your explanation makes sense to me and the patch looks good. Reviewed-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
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