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

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Message-ID: <20200414124132.GV3456981@phenom.ffwll.local>
Date:   Tue, 14 Apr 2020 14:41:32 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Yussuf Khalil <dev@...345.net>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        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 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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch