[Intel-gfx] [v2 0/7] Add Multi Segment Gamma Support

Mon Apr 8 16:07:40 UTC 2019

On Mon, Apr 08, 2019 at 03:59:51PM +0000, Shankar, Uma wrote:
> 
> 
> >-----Original Message-----
> >From: dri-devel [mailto:dri-devel-bounces at lists.freedesktop.org] On Behalf Of Ville
> >Syrjälä
> >Sent: Monday, April 8, 2019 9:15 PM
> >To: Shankar, Uma <uma.shankar at intel.com>
> >Cc: dcastagna at chromium.org; intel-gfx at lists.freedesktop.org; dri-
> >devel at lists.freedesktop.org; seanpaul at chromium.org; Syrjala, Ville
> ><ville.syrjala at intel.com>; Lankhorst, Maarten <maarten.lankhorst at intel.com>
> >Subject: Re: [Intel-gfx] [v2 0/7] Add Multi Segment Gamma Support
> >
> >On Mon, Apr 08, 2019 at 03:40:39PM +0000, Shankar, Uma wrote:
> >>
> >>
> >> >-----Original Message-----
> >> >From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
> >> >Sent: Monday, April 8, 2019 8:27 PM
> >> >To: Shankar, Uma <uma.shankar at intel.com>
> >> >Cc: dcastagna at chromium.org; intel-gfx at lists.freedesktop.org; dri-
> >> >devel at lists.freedesktop.org; seanpaul at chromium.org; Syrjala, Ville
> >> ><ville.syrjala at intel.com>; Lankhorst, Maarten
> >> ><maarten.lankhorst at intel.com>
> >> >Subject: Re: [Intel-gfx] [v2 0/7] Add Multi Segment Gamma Support
> >> >
> >> >On Mon, Apr 08, 2019 at 02:40:51PM +0000, Shankar, Uma wrote:
> >> >>
> >> >>
> >> >> >-----Original Message-----
> >> >> >From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
> >> >> >Sent: Monday, April 8, 2019 6:01 PM
> >> >> >To: Shankar, Uma <uma.shankar at intel.com>
> >> >> >Cc: dcastagna at chromium.org; intel-gfx at lists.freedesktop.org; dri-
> >> >> >devel at lists.freedesktop.org; seanpaul at chromium.org; Syrjala, Ville
> >> >> ><ville.syrjala at intel.com>; Lankhorst, Maarten
> >> >> ><maarten.lankhorst at intel.com>
> >> >> >Subject: Re: [Intel-gfx] [v2 0/7] Add Multi Segment Gamma Support
> >> >> >
> >> >> >On Mon, Apr 08, 2019 at 12:26:23PM +0000, Shankar, Uma wrote:
> >> >> >>
> >> >> >>
> >> >> >> >-----Original Message-----
> >> >> >> >From: dri-devel
> >> >> >> >[mailto:dri-devel-bounces at lists.freedesktop.org]
> >> >> >> >On Behalf Of Ville Syrjälä
> >> >> >> >Sent: Friday, April 5, 2019 9:42 PM
> >> >> >> >To: Shankar, Uma <uma.shankar at intel.com>
> >> >> >> >Cc: dcastagna at chromium.org; intel-gfx at lists.freedesktop.org;
> >> >> >> >dri- devel at lists.freedesktop.org; seanpaul at chromium.org;
> >> >> >> >Syrjala, Ville <ville.syrjala at intel.com>; Lankhorst, Maarten
> >> >> >> ><maarten.lankhorst at intel.com>
> >> >> >> >Subject: Re: [Intel-gfx] [v2 0/7] Add Multi Segment Gamma
> >> >> >> >Support
> >> >> >> >
> >> >> >> >On Mon, Apr 01, 2019 at 11:00:04PM +0530, Uma Shankar wrote:
> >> >> >> >> This series adds support for programmable gamma modes and
> >> >> >> >> exposes a property interface for the same. Also added,
> >> >> >> >> support for multi segment gamma mode introduced in ICL+
> >> >> >> >>
> >> >> >> >> It creates 2 property interfaces :
> >> >> >> >> 1. GAMMA_MODE_CAPS: This is immutable property and exposes
> >> >> >> >> the various gamma modes supported and the lut ranges. This is
> >> >> >> >> an enum property with element as blob id. Getting the blob id
> >> >> >> >> in userspace, user can get the mode supported and also the
> >> >> >> >> range of gamma mode supported with number of lut coefficients.
> >> >> >> >>
> >> >> >> >> 2. GAMMA_MODE: This is for user to set the gamma mode and
> >> >> >> >> send the lut values for that particular mode.
> >> >> >> >
> >> >> >> >I think we should just go for the BLOB_ENUM prop type instead.
> >> >> >> >Then the possible values and the current value are all part of the same prop.
> >> >> >>
> >> >> >> Hi Ville,
> >> >> >> With the current approach, we have enum property with values as
> >> >> >> blob_ids (representing platform capabilities). This should not
> >> >> >> get modified and needs to be immutable.
> >> >> >
> >> >> >That's not quite what we want. We want to let the user modify the
> >> >> >current value so that they can actually select the gamma mode.
> >> >> >Otherwise we need yet another prop for it, or we have to deduce it
> >> >> >from the LUT size (that apporach would actually work for i915 but
> >> >> >may not work for other drivers/hardware).
> >> >> >
> >> >> >>
> >> >> >> Userspace can query the property and get the blob using the blob_ids.
> >> >> >> Thereby getting all the platform capabilities.
> >> >> >>
> >> >> >> Now to set the LUT values, he can use another blob property and
> >> >> >> pass the luts.  This is inline to how gamma/degamma is
> >> >> >> implemented where we have one immutable LUT_SIZE property
> >> >> >> (indicating number of
> >> >> >> luts) and another blob property for actual lut values..
> >> >>
> >> >> Hi Ville,
> >> >> Just to clarify and clear some doubts :)
> >> >>
> >> >> We should be able to set the gamma mode using the blob enum value.
> >> >> Userspace will get the list enum vals (blob ids with mode name
> >> >> embedded) and
> >> >select one and do a setprop to set a mode.
> >> >> Driver will get the blob_id and will be able to get the mode to be
> >> >> set.  So exposing capabilities and setting the mode should be
> >> >> possible with this one
> >> >property. I hope my understanding is correct.
> >> >>
> >> >> Now to send the actual blob values to be set, we need to use some
> >> >> other property interface. Should we use the currently available
> >> >> "gamma blob
> >> >(gamma_lut_property)" property to send the lut values.
> >> >> The challenge there is that it currently uses 16 bit lut values
> >> >> struct drm_color_lut {
> >> >>         __u16 red;
> >> >>         __u16 green;
> >> >>         __u16 blue;
> >> >>         __u16 reserved;
> >> >> };
> >> >> which is not sufficient for HDR usecases. Or should we need a new
> >> >> property for
> >> >advance lut/extended lut like below:
> >> >> https://patchwork.freedesktop.org/patch/294732/?series=30875&rev=7
> >> >>
> >> >> What do you suggest ?
> >> >
> >> >I was thinking that we might get away with reusing the current props
> >> >and just change the interpretation of the data when gamma_mode is
> >> >set. But I'm not sure that's going to work out so well if one client
> >> >sets this up and then another client comes along that doesn't
> >> >understand the new props at all. But even with separate props I think
> >> >we might still end up in a mess because the new client wouldn't know
> >> >how to unset the higher precision LUT before setting up the old style prop and the
> >kernel would then refuse the operation with with both props being set.
> >> >
> >> >So I think we might need a client cap for this which simply changes
> >> >how the data in the existing props is represented. So internally we
> >> >could always store things in the new high precision format, but we'd
> >> >convert to/from the old format when dealing with an older client.
> >>
> >> We could also say that if a legacy gamma_mode_property is set (which
> >> will be used by legacy apps or apps not aware of new interface), in
> >> driver we will simply unset the earlier gamma_mode and fallback to
> >> legacy mode (whatever it was for a particular platform). This way we
> >> should be able to deal with this situation and an explicit unset may not be needed.
> >What do you think ?
> >
> >I don't want (non-immutable) properties that magically change values.
> >That way lies madness.
> 
> Oh ok. So do you suggest that we add some kind of  flag to be set by user, based on
> which we take either legacy or advance_gamma path. Is my understanding correct ?

Yeah, just another client cap. I can't immediately think of a nicer way
to extend the precision.

-- 
Ville Syrjälä
Intel