On Wed, Jun 18, 2025 at 08:30:39AM +0200, Marek Szyprowski wrote: > On 16.06.2025 17:40, Tomi Valkeinen wrote: > > On 12/06/2025 09:31, Marek Szyprowski wrote: > >> On 12.06.2025 07:49, Tomi Valkeinen wrote: > >>> On 11/06/2025 13:45, Marek Szyprowski wrote: > >>>> On 05.06.2025 19:15, Aradhya Bhatia wrote: > >>>>> From: Aradhya Bhatia <[email protected]> > >>>>> > >>>>> Move the bridge pre_enable call before crtc enable, and the bridge > >>>>> post_disable call after the crtc disable. > >>>>> > >>>>> The sequence of enable after this patch will look like: > >>>>> > >>>>> bridge[n]_pre_enable > >>>>> ... > >>>>> bridge[1]_pre_enable > >>>>> > >>>>> crtc_enable > >>>>> encoder_enable > >>>>> > >>>>> bridge[1]_enable > >>>>> ... > >>>>> bridge[n]_enable > >>>>> > >>>>> And, the disable sequence for the display pipeline will look like: > >>>>> > >>>>> bridge[n]_disable > >>>>> ... > >>>>> bridge[1]_disable > >>>>> > >>>>> encoder_disable > >>>>> crtc_disable > >>>>> > >>>>> bridge[1]_post_disable > >>>>> ... > >>>>> bridge[n]_post_disable > >>>>> > >>>>> The definition of bridge pre_enable hook says that, > >>>>> "The display pipe (i.e. clocks and timing signals) feeding this bridge > >>>>> will not yet be running when this callback is called". > >>>>> > >>>>> Since CRTC is also a source feeding the bridge, it should not be enabled > >>>>> before the bridges in the pipeline are pre_enabled. Fix that by > >>>>> re-ordering the sequence of bridge pre_enable and bridge post_disable. > >>>>> > >>>>> While at it, update the drm bridge API documentation as well. > >>>>> > >>>>> Acked-by: Dmitry Baryshkov <[email protected]> > >>>>> Reviewed-by: Tomi Valkeinen <[email protected]> > >>>>> Reviewed-by: Thomas Zimmermann <[email protected]> > >>>>> Tested-by: Tomi Valkeinen <[email protected]> > >>>>> Tested-by: Alexander Sverdlin <[email protected]> > >>>>> Signed-off-by: Aradhya Bhatia <[email protected]> > >>>>> Signed-off-by: Aradhya Bhatia <[email protected]> > >>>> This patch landed in today's linux-next as commit c9b1150a68d9 > >>>> ("drm/atomic-helper: Re-order bridge chain pre-enable and > >>>> post-disable"). In my tests I found that it breaks booting of Samsung > >>>> Exynos 5420/5800 based Chromebooks (Peach-Pit and Peach-Pi). Both of > >>>> them use Exynos DRM with Exynos_DP sub-driver (Analogix DP) and EDP > >>>> panel. Booting stops at '[drm] Initialized exynos 1.1.0 for exynos-drm > >>>> on minor 0' message. On the other hand, the Samsung Exynos5250 based > >>>> Snow Chromebook boots fine, but it uses dp-lvds nxp,ptn3460 bridge and > >>>> lvds panel instead of edp panels. This looks like some sort of deadlock, > >>>> because if I disable FBDEV emulation, those boards boots fine and I'm > >>>> able to run modetest and enable the display. Also the DRM kernel logger > >>>> seems to be working fine, although I didn't check the screen output yet, > >>>> as I only have a remote access to those boards. I will investigate it > >>>> further and let You know. > >>> Thanks for the report. I was trying to understand the pipeline, but I'm > >>> a bit confused. Above you say Peach-Pit uses DP and EDP panel, but if I > >>> look at arch/arm/boot/dts/samsung/exynos5420-peach-pit.dts, it connects > >>> a dp->lvds bridge (parade,ps8625). Peach-Pi seems to connect to an eDP > >>> panel. > >>> > >>> Is the above correct? Do both Peach-Pi and Peach-Pit fail? > >> Yes, sorry, my fault. I much have checked the same (peach-pi) dts 2 > >> times. Both Peach-Pi and Peach-Pit fails, while Snow works fine. All > >> three use the same Exynos DP (based on analogix dp) driver. I will try > >> to play a bit more with those boards in the afternoon, hopefully getting > >> some more hints where the issue is. > > Did you get a chance to test this more? Any hints what happens will help =) > > I've spent some time debugging this issue, but so far I only got > something I don't really understand. This issue is somehow related with > the DP clock enabling and disabling, what is being done from > exynos_dp_poweron() and exynos_dp_poweroff() functions, which are called > from analogix_dp_resume() and analogix_dp_suspend(). The lockup happens > somewhere while registering the fbdev console, with console lock held, > what makes debugging much harder.
You can skip the locking part with the fb.lockless_register_fb=1 kernel parameter. It's of course not meant for anything but debugging, but it's useful :) Maxime
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