Hi Daniel,
On 11-11-2019 11:26, Daniel Vetter wrote:
On Mon, Nov 11, 2019 at 10:50 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
Hi,
On 11-11-2019 10:25, Daniel Vetter wrote:
On Sun, Nov 10, 2019 at 7:41 PM Hans de Goede <hdegoede@xxxxxxxxxx> 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@xxxxxxxxxx>
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@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@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@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?
The idea is to not automatically fix this, all I want to do is
provide enough info to userspace to make an informed decision,
plymouth honored the video= resolution, we want to
preserve that behavior.
Likewise historically and currently compositors / Xorg pretty
much ignore video=, I do not want to introduce changes on the
kernel side which unilateral force a change here. If compositors
want to start honoring a video= provided/selected mode then that
is up to them.
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.
Right, I considered using PREFERRED instead (and clearing it on other
modes) and I deliberately did not do this. You say:
"Changing the meaning of USERDEF to also mean
"preferred mode, pls use that" could be fraught with peril"
But since no userspace currently checks for USERDEF (*) it means that
adding the flag will not cause anything to change. Where as adding
PREFERRED will all of a sudden cause compositors/Xorg to pick a
different default resolution. Arguably that is desirable, but it
is an ABI breaks of sort and I'm sure some users will be using
video=XXXxYYY to set a lower-resolution for fbcon (e.g. for readability
on HiDPI) and will not appreciate it if their compositor now also
picks this resolution.
So as said the purpose of this patch is not too change anything,
but only to pass info to userspace that this mode was set for the
connector through video= on the kernel commandline.
Alternatively we could add a new USERSELECTED flag and set that
when we are not adding a new CVT/GTF mode since one of the probed
modes already provides the requested resolution.
Basically my goal is to get the info about the mode passed
for the connector through video=name:XXXxYYY to userspace without
userspace having to have its own copy of the video= parsing code.
I hope this clarifies things.
Regards,
Hans
*) For the pending plymouth patch the behavior change is desirable,
as it keeps plymouth's historical behavior of honoring video=
-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
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