linux-kernel - Re: [PATCH 1/5] drm/modes: Indicate CEA-861 CE modes to user-space

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Message-ID: <20200417145755.GL3456981@phenom.ffwll.local>
Date:   Fri, 17 Apr 2020 16:57:55 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Yussuf Khalil <dev@...345.net>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] drm/modes: Indicate CEA-861 CE modes to user-space

On Thu, Apr 16, 2020 at 03:51:36PM +0200, Yussuf Khalil wrote:
> On Tue, 2020-04-14 at 14:41 +0200, Daniel Vetter wrote:
> > On Mon, Apr 13, 2020 at 11:40:22PM +0200, Yussuf Khalil wrote:
> > > Add a new flag to mark modes that are considered a CE mode
> > > according to the
> > > CEA-861 specification. Modes without this flag are implicitly
> > > considered to
> > > be IT modes.
> > > 
> > > User-space applications may use this flag to determine possible
> > > implications of using a CE mode (e.g., limited RGB range).
> > > 
> > > There is no use for this flag inside the kernel, so we set it only
> > > when
> > > communicating a mode to user-space.
> > > 
> > > Signed-off-by: Yussuf Khalil <dev@...345.net>
> > 
> > Do we have userspace for this?
> > 
> > If we go with the existing quant range property you don't need new
> > userspace for the property itself. But this flag here is new uapi, so
> > needs userspace per
> > 
> > https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements
> > 
> > Also since this standardizes kms uapi, we need testcases per
> > 
> > https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#testing-requirements-for-userspace-api
> > 
> > Cheers, Daniel
> > 
> > > ---
> > >  drivers/gpu/drm/drm_modes.c | 14 ++++++++++++++
> > >  include/uapi/drm/drm_mode.h |  2 ++
> > >  2 files changed, 16 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_modes.c
> > > b/drivers/gpu/drm/drm_modes.c
> > > index d4d64518e11b..0d8a032f437d 100644
> > > --- a/drivers/gpu/drm/drm_modes.c
> > > +++ b/drivers/gpu/drm/drm_modes.c
> > > @@ -1973,6 +1973,14 @@ void drm_mode_convert_to_umode(struct
> > > drm_mode_modeinfo *out,
> > >  		break;
> > >  	}
> > >  
> > > +	if (drm_match_cea_mode(in) > 1) {
> > > +		/*
> > > +		 * All modes in CTA-861-G Table 1 are CE modes, except
> > > 640x480p
> > > +		 * (VIC 1).
> > > +		 */
> > > +		out->flags |= DRM_MODE_FLAG_CEA_861_CE_MODE;
> > > +	}
> > > +
> > >  	strncpy(out->name, in->name, DRM_DISPLAY_MODE_LEN);
> > >  	out->name[DRM_DISPLAY_MODE_LEN-1] = 0;
> > >  }
> > > @@ -2045,6 +2053,12 @@ int drm_mode_convert_umode(struct drm_device
> > > *dev,
> > >  		return -EINVAL;
> > >  	}
> > >  
> > > +	/*
> > > +	 * The CEA-861 CE mode flag is purely informational and
> > > intended for
> > > +	 * userspace only.
> > > +	 */
> > > +	out->flags &= ~DRM_MODE_FLAG_CEA_861_CE_MODE;
> > > +
> > >  	out->status = drm_mode_validate_driver(dev, out);
> > >  	if (out->status != MODE_OK)
> > >  		return -EINVAL;
> > > diff --git a/include/uapi/drm/drm_mode.h
> > > b/include/uapi/drm/drm_mode.h
> > > index 735c8cfdaaa1..5e78b350b2e2 100644
> > > --- a/include/uapi/drm/drm_mode.h
> > > +++ b/include/uapi/drm/drm_mode.h
> > > @@ -124,6 +124,8 @@ extern "C" {
> > >  #define  DRM_MODE_FLAG_PIC_AR_256_135 \
> > >  			(DRM_MODE_PICTURE_ASPECT_256_135<<19)
> > >  
> > > +#define DRM_MODE_FLAG_CEA_861_CE_MODE (1<<23)
> > > +
> > >  #define  DRM_MODE_FLAG_ALL	(DRM_MODE_FLAG_PHSYNC |		\
> > >  				 DRM_MODE_FLAG_NHSYNC |		\
> > >  				 DRM_MODE_FLAG_PVSYNC |		\
> > > -- 
> > > 2.26.0
> > > 
> 
> Sorry, I wasn't aware DRM had these additional requirements. I do have a user-
> space implementation in mutter and gnome-control-center that makes use of the
> new property and this flag on my local machine. I'll try to propose the branch
> upstream before sending in the next revision of this patchset.
> 
> Do I understand it correctly that this will require test cases for both the
> property itself and the new flag? I'll write a patch for IGT then.

Yup. We even have some edid injection stuff so you can (for some value of
"can") test this on systems without such a monitor. That would obviously
be the gold standard for this, so that CI systems can make sure we don't
break any of this in the driver side.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch