How to map depth=30 fb to XBGR instead of XRGB?

How to map depth=30 fb to XBGR instead of XRGB?

[Ilia Mirkin]

NVIDIA hardware, prior to Kepler, only supports XBGR2101010. However
drmAddFB with depth = 30 will use the mapping in
drm_mode_legacy_fb_format and pick the XRGB version of the format.

One solution is to tell userspace "stop using addfb, move to addfb2".
However I'm hoping that there's some sort of semi-clean way of dealing
with such driver eccentricities without resorting to changing
userspace.

Can the ioctl be handled in the driver perhaps? Or would it be
reasonable to add a callback in drm_driver?

Suggestions welcome.

  -ilia
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Re: How to map depth=30 fb to XBGR instead of XRGB?

[Ville Syrjälä]

On Sun, Dec 31, 2017 at 01:03:39AM -0500, Ilia Mirkin wrote:
> NVIDIA hardware, prior to Kepler, only supports XBGR2101010. However
> drmAddFB with depth = 30 will use the mapping in
> drm_mode_legacy_fb_format and pick the XRGB version of the format.
> 
> One solution is to tell userspace "stop using addfb, move to addfb2".
> However I'm hoping that there's some sort of semi-clean way of dealing
> with such driver eccentricities without resorting to changing
> userspace.
> 
> Can the ioctl be handled in the driver perhaps? Or would it be
> reasonable to add a callback in drm_driver?

I don't think there's any sane way to allow the driver to remap these.
How would generic userspace know which component order the driver
actually picked?

-- 
Ville Syrjälä
Intel OTC
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Re: How to map depth=30 fb to XBGR instead of XRGB?

[Chris Wilson]

Quoting Ville Syrjälä (2018-01-09 15:19:06)
> On Sun, Dec 31, 2017 at 01:03:39AM -0500, Ilia Mirkin wrote:
> > NVIDIA hardware, prior to Kepler, only supports XBGR2101010. However
> > drmAddFB with depth = 30 will use the mapping in
> > drm_mode_legacy_fb_format and pick the XRGB version of the format.
> > 
> > One solution is to tell userspace "stop using addfb, move to addfb2".
> > However I'm hoping that there's some sort of semi-clean way of dealing
> > with such driver eccentricities without resorting to changing
> > userspace.
> > 
> > Can the ioctl be handled in the driver perhaps? Or would it be
> > reasonable to add a callback in drm_driver?
> 
> I don't think there's any sane way to allow the driver to remap these.
> How would generic userspace know which component order the driver
> actually picked?

With getfb? Wait, I'll get my coat.
-Chris
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Re: How to map depth=30 fb to XBGR instead of XRGB?

[Daniel Vetter]

On Tue, Jan 09, 2018 at 03:28:23PM +0000, Chris Wilson wrote:
> Quoting Ville Syrjälä (2018-01-09 15:19:06)
> > On Sun, Dec 31, 2017 at 01:03:39AM -0500, Ilia Mirkin wrote:
> > > NVIDIA hardware, prior to Kepler, only supports XBGR2101010. However
> > > drmAddFB with depth = 30 will use the mapping in
> > > drm_mode_legacy_fb_format and pick the XRGB version of the format.
> > > 
> > > One solution is to tell userspace "stop using addfb, move to addfb2".
> > > However I'm hoping that there's some sort of semi-clean way of dealing
> > > with such driver eccentricities without resorting to changing
> > > userspace.
> > > 
> > > Can the ioctl be handled in the driver perhaps? Or would it be
> > > reasonable to add a callback in drm_driver?
> > 
> > I don't think there's any sane way to allow the driver to remap these.
> > How would generic userspace know which component order the driver
> > actually picked?
> 
> With getfb? Wait, I'll get my coat.

debugfs would dump the actual pixel format, at least in 4.16 :-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: How to map depth=30 fb to XBGR instead of XRGB?

[Daniel Vetter]

On Tue, Jan 09, 2018 at 05:19:06PM +0200, Ville Syrjälä wrote:
> On Sun, Dec 31, 2017 at 01:03:39AM -0500, Ilia Mirkin wrote:
> > NVIDIA hardware, prior to Kepler, only supports XBGR2101010. However
> > drmAddFB with depth = 30 will use the mapping in
> > drm_mode_legacy_fb_format and pick the XRGB version of the format.
> > 
> > One solution is to tell userspace "stop using addfb, move to addfb2".
> > However I'm hoping that there's some sort of semi-clean way of dealing
> > with such driver eccentricities without resorting to changing
> > userspace.
> > 
> > Can the ioctl be handled in the driver perhaps? Or would it be
> > reasonable to add a callback in drm_driver?
> 
> I don't think there's any sane way to allow the driver to remap these.
> How would generic userspace know which component order the driver
> actually picked?

By using addfb2. That seems the only option, and it'll likely result in a
bunch more "nouveau is crap" forum posts when people try to use 30bpp
with generic userspace on nouveau. Best we can do is drop a info_once
message into dmesg that userspace should consider using addfb2.

Ilia said he's ok with more "nouveau is crap", and that's about the only
option we have any.

Wrt implementation: A flag in drm_mode_config that overwrites the choice
in drm_addfb_ioctl (so that we can avoid going through all the drivers),
plus the same hack in the fbdev probe callback in nouveau is probably the
least invasive. Core one with a very huge comment ofc.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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