[PATCH] drm: Add DRM_MODE_TYPE_USERDEF flag to probed modes matching a video= argument
Daniel Vetter
daniel at ffwll.ch
Mon Nov 11 10:26:43 UTC 2019
On Mon, Nov 11, 2019 at 10:50 AM Hans de Goede <hdegoede at redhat.com> wrote:
>
> Hi,
>
> On 11-11-2019 10:25, Daniel Vetter wrote:
> > On Sun, Nov 10, 2019 at 7:41 PM Hans de Goede <hdegoede at redhat.com> wrote:
> >>
> >> drm_helper_probe_add_cmdline_mode() prefers using a probed mode matching
> >> a video= argument over calculating our own timings for the user specified
> >> mode using CVT or GTF.
> >>
> >> But userspace code which is auto-configuring the mode may want to know that
> >> the user has specified that mode on the kernel commandline so that it can
> >> pick that mode over the mode which is marked as DRM_MODE_TYPE_PREFERRED.
> >>
> >> This commit sets the DRM_MODE_TYPE_USERDEF flag on the matching mode, just
> >> as we would do on the user-specified mode when no matching probed mode is
> >> found.
> >>
> >> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >
> > Will existing userspace dtrt here with this? Some links to popular
> > ones would be good (since essentially this is uapi fine tuning we need
> > that anyway). With that will get my ack.
>
> A valid question, I've gone over what I consider the major userspace kms users:
> -Xorg xserver modesetting driver does not check for this:
> [hans at shalem xserver]$ ack DRM_MODE_TYPE_ hw/xfree86/drivers/modesetting/
> hw/xfree86/drivers/modesetting/drmmode_display.c
> 1321: if (kmode->type & DRM_MODE_TYPE_DRIVER)
> 1323: if (kmode->type & DRM_MODE_TYPE_PREFERRED)
> -Other Xorg drivers:
> [hans at shalem driver]$ ls -d xf86-video-*
> xf86-video-amdgpu xf86-video-intel xf86-video-qxl
> xf86-video-armsoc xf86-video-modesetting xf86-video-sisusb
> xf86-video-ati xf86-video-nouveau xf86-video-vmware
> xf86-video-dummy xf86-video-omap xf86-video-voodoo
> xf86-video-geode xf86-video-opentegra
> These all only do the same checks as the Xorg modesetting driver
> -mutter:
> [hans at shalem mutter]$ ack DRM_MODE_TYPE_
> src/backends/native/meta-output-kms.c
> 261: if (drm_mode->type & DRM_MODE_TYPE_PREFERRED)
>
> So it seems nothing (that I can quickly find) in userspace is using this atm.
>
> The reason I wrote this patch is because about a year ago plymouth used to
> fully rely on the kernel to setup the modes on monitors and would simply
> inherit the modes setup by the kernel. Basically plymouth was relying on
> fbcon to load first and setup modes.
>
> Deferred fbcon takeover (for flickerfree) means that this is no longer
> happening. So now plymouth picks a mode itself. When I submitted the
> plymouth change for plymouth to pick a mode itself the plymouth maintainer
> (Ray Strode) was afraid that would break plymouth honoring video= arguments.
> So currently plymouth still relies on the kernel to do the mode setup if
> a video= argument is present on the kernel commandline.
>
> My other recent series, which adds support for e.g.
> video=HDMI:panel_orientation=right_side_up, made me realize that relying
> on the kernel for this is no good since the fbcon code has various
> limitations wrt e.g. hotplug and this of course will not work when
> fbcon deferred takeover is used and fbcon never loads before plymouth.
>
> So I wrote a patch for plymouth to check the DRM_MODE_TYPE_USERDEF
> flag and prefer a mode with that flag over the PREFERRED mode:
> https://gitlab.freedesktop.org/plymouth/plymouth/merge_requests/84
>
> And then I found out that for that code to work with modes which
> are already in the list of probed modes, I need something like
> the kernel patch we are discussing now.
>
> So if you want a link to an userspace consumer of this, I guess you
> want a v2 with a link to the plymouth MR added. + maybe a blurb in
> the commit message that to the best of my knowledge no userspace
> kms consumers are checking for the DRM_MODE_TYPE_USERDEF flag?
And how does just relying on plymouth fix this?
Given what you figured out in your quick search I think we should set
both USERDEF and PREFERRED, otherwise not much will happen here. Plus
I guess we need some fixup code to make sure that only the cmdline
mode is preferred, and no other mode? Except if all compositors pick
the first preferred mode consistently, then I guess we just need to
make sure it's first. Changing the meaning of USERDEF to also mean
"preferred mode, pls use that" could be fraught with peril, e.g. you
run a game on an old compositor (or with direct display) at lower
refresh, maybe with a custom mode, then it crashes. And from then on
all compositors insist on using your "preferred" mode.
-Daniel
>
> Regards,
>
> Hans
>
>
>
>
>
>
> > -Danile
> >
> >> ---
> >> drivers/gpu/drm/drm_probe_helper.c | 2 ++
> >> include/drm/drm_modes.h | 3 ++-
> >> 2 files changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> >> index ef2c468205a2..4fed64be11f9 100644
> >> --- a/drivers/gpu/drm/drm_probe_helper.c
> >> +++ b/drivers/gpu/drm/drm_probe_helper.c
> >> @@ -157,6 +157,8 @@ static int drm_helper_probe_add_cmdline_mode(struct drm_connector *connector)
> >> continue;
> >> }
> >>
> >> + /* Mark the matching mode as being preferred by the user */
> >> + mode->type |= DRM_MODE_TYPE_USERDEF;
> >> return 0;
> >> }
> >>
> >> diff --git a/include/drm/drm_modes.h b/include/drm/drm_modes.h
> >> index e946e20c61d8..c7efb7487e9b 100644
> >> --- a/include/drm/drm_modes.h
> >> +++ b/include/drm/drm_modes.h
> >> @@ -256,7 +256,8 @@ struct drm_display_mode {
> >> * - DRM_MODE_TYPE_DRIVER: Mode created by the driver, which is all of
> >> * them really. Drivers must set this bit for all modes they create
> >> * and expose to userspace.
> >> - * - DRM_MODE_TYPE_USERDEF: Mode defined via kernel command line
> >> + * - DRM_MODE_TYPE_USERDEF: Mode defined or selected via the kernel
> >> + * command line.
> >> *
> >> * Plus a big list of flags which shouldn't be used at all, but are
> >> * still around since these flags are also used in the userspace ABI.
> >> --
> >> 2.23.0
> >>
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel at lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
> >
> >
>
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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