[PATCH 1/9] drm: Add gamma mode property

[Shankar, Uma]

> -----Original Message-----
> From: Pekka Paalanen <ppaalanen at gmail.com>
> Sent: Wednesday, June 2, 2021 2:40 PM
> To: Shankar, Uma <uma.shankar at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org; Modem,
> Bhanuprakash <bhanuprakash.modem at intel.com>
> Subject: Re: [PATCH 1/9] drm: Add gamma mode property
> 
> On Tue,  1 Jun 2021 16:11:27 +0530
> Uma Shankar <uma.shankar at intel.com> wrote:
> 
> > Add a gamma mode property to enable various kind of gamma modes
> > supported by platforms like: Interpolated, Split, Multi Segmented,
> > Logarithmic etc. Userspace can get this property and should be able to
> > get the platform capabilities wrt various gamma modes possible and the
> > possible ranges.
> >
> > It can select one of the modes exposed as blob_id as an enum and set
> > the respective mode.
> >
> > It can then create the LUT and send it to driver using already
> > available GAMMA_LUT property as blob.
> >
> > Note: This is based on design by Ville and is being carried forward
> > based on his original idea.
> >
> > Signed-off-by: Uma Shankar <uma.shankar at intel.com>
> > ---
> >  drivers/gpu/drm/drm_atomic_uapi.c |  5 +++
> > drivers/gpu/drm/drm_color_mgmt.c  | 75 +++++++++++++++++++++++++++++++
> >  include/drm/drm_color_mgmt.h      |  8 ++++
> >  include/drm/drm_crtc.h            | 14 ++++++
> >  include/uapi/drm/drm_mode.h       | 43 ++++++++++++++++++
> >  5 files changed, 145 insertions(+)
> >
> 
> ...
> 
> > diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index
> > 13eeba2a750a..b1eead03ebe8 100644
> > --- a/include/drm/drm_crtc.h
> > +++ b/include/drm/drm_crtc.h
> > @@ -262,6 +262,13 @@ struct drm_crtc_state {
> >  	 */
> >  	struct drm_property_blob *mode_blob;
> >
> > +	/**
> > +	 * @gamma_mode: This is a blob_id and exposes the platform capabilities
> > +	 * wrt to various gamma modes and the respective lut ranges. This also
> > +	 * helps user select a gamma mode amongst the supported ones.
> > +	 */
> > +	u32 gamma_mode;
> > +
> >  	/**
> >  	 * @degamma_lut:
> >  	 *
> > @@ -1096,6 +1103,13 @@ struct drm_crtc {
> >  	 */
> >  	struct drm_property *scaling_filter_property;
> >
> > +	/**
> > +	 * @gamma_mode_property: Optional CRTC property to enumerate and
> > +	 * select the mode of the crtc gamma/degmama LUTs. This also exposes
> > +	 * the lut ranges of the various supported gamma modes to userspace.
> > +	 */
> > +	struct drm_property *gamma_mode_property;
> > +
> >  	/**
> >  	 * @state:
> >  	 *
> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index 9b6722d45f36..d7758d351936 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -819,6 +819,49 @@ struct hdr_output_metadata {
> >  	};
> >  };
> >
> > +/*
> > + * DRM_MODE_LUT_GAMMA|DRM_MODE_LUT_DEGAMMA is legal and means
> the LUT
> > + * can be used for either purpose, but not simultaneously. To expose
> > + * modes that support gamma and degamma simultaneously the gamma mode
> > + * must declare distinct DRM_MODE_LUT_GAMMA and
> DRM_MODE_LUT_DEGAMMA
> > + * ranges.
> > + */
> > +/* LUT is for gamma (after CTM) */
> > +#define DRM_MODE_LUT_GAMMA BIT(0)
> > +/* LUT is for degamma (before CTM) */ #define DRM_MODE_LUT_DEGAMMA
> > +BIT(1)
> > +/* linearly interpolate between the points */ #define
> > +DRM_MODE_LUT_INTERPOLATE BIT(2)
> > +/*
> > + * the last value of the previous range is the
> > + * first value of the current range.
> > + */
> > +#define DRM_MODE_LUT_REUSE_LAST BIT(3)
> > +/* the curve must be non-decreasing */ #define
> > +DRM_MODE_LUT_NON_DECREASING BIT(4)
> > +/* the curve is reflected across origin for negative inputs */
> > +#define DRM_MODE_LUT_REFLECT_NEGATIVE BIT(5)
> > +/* the same curve (red) is used for blue and green channels as well
> > +*/ #define DRM_MODE_LUT_SINGLE_CHANNEL BIT(6)
> > +
> > +struct drm_color_lut_range {
> > +	/* DRM_MODE_LUT_* */
> > +	__u32 flags;
> > +	/* number of points on the curve */
> > +	__u16 count;
> > +	/* input/output bits per component */
> > +	__u8 input_bpc, output_bpc;
> > +	/* input start/end values */
> > +	__s32 start, end;
> > +	/* output min/max values */
> > +	__s32 min, max;
> > +};
> > +
> > +enum lut_type {
> > +	LUT_TYPE_DEGAMMA = 0,
> > +	LUT_TYPE_GAMMA = 1,
> > +};
> > +
> >  #define DRM_MODE_PAGE_FLIP_EVENT 0x01  #define
> > DRM_MODE_PAGE_FLIP_ASYNC 0x02  #define
> > DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4
> 
> Hi,
> 
> where is the UAPI documentation for this new GAMMA_MODE?
> As a userspace dev, I have no idea what to do with the above based on what's
> written here.

Got that, I will add more details on the UAPI usage to make things a bit clearer.

> Also, reading the description of DRM_CLIENT_CAP_ADVANCE_GAMMA_MODES in
> patch 5/9, what difference does it make whether userspace sets or does not set that
> cap? I don't understand the implications from the description.

The reason we have this Client caps is to have it co-exist with legacy crtc color properties.
The idea is that driver will describe the h/w luts to userspace through GAMMA_MODE UAPI,
but the actual lut samples will still be sent through the legacy GAMMA_LUT UAPI. This client
cap will help distinguish between legacy and this new implementation.

I will add more details in the UAPI description to avoid ambiguity and explain the rationale and
usage of this UAPI.

Thanks Pekka for the looking into the series and the initial feedback.

Regards,
Uma Shankar

> 
> Thanks,
> pq