[Intel-gfx] Design review request: DRM color manager

[Thierry Reding]

On Tue, May 13, 2014 at 09:18:45AM +0530, Sharma, Shashank wrote:
> Daniel,
> Please find my comments inline.
> 
> Regards
> Shashank
> On 5/12/2014 8:58 PM, Daniel Vetter wrote:
> >On Mon, May 12, 2014 at 05:35:13PM +0530, Sharma, Shashank wrote:
> >>Thanks for your time and the comments David.
> >>please find mine inline.
> >>
> >>Regards
> >>Shashank
> >>On 5/12/2014 5:20 PM, David Herrmann wrote:
> >>>Hi
> >>>
> >>>On Mon, May 12, 2014 at 12:26 PM, Sharma, Shashank
> >>><shashank.sharma at intel.com> wrote:
> >Gamma correction lut is already supported. For the other stuff we can use
> >SET_BLOB (or fix it if it doesn't work).
> >
> Current gamma correction supports only 8 bit mode, which cant do a real
> gamma correction. This is only to initialize the LUT. Actual gamma
> correction needs 10 bit support.
> 
> As discussed in design, the idea is same, ie to fix (implement) SET_BLOB.
> But see some of the requirements on LUT size of VLV:
> 
> 1. Gamma correction: 256 values
> 2. CSC : 9 values in form of 6 register
> 3. Hue : 1 value (Plane level)
> 4. Saturation: 1 value (Plane level)
> 5. Contrast: 1 value (Plane level)
> 6. Brightness: 1 value (Plane level)
> 
> For CHV, the requirement is again different.
> There are different values, which vary from platform to platform and
> property-by-property.
> Now, one method of supporting these values is create a DRM property for
> each, some blob, some single valued, set individual interface and set them
> all at random. IMHO, this looks the non-systematic way of doing it.

That's exactly what atomic modeset/pageflip is meant to address. You get
the flexibility of individual properties and on top of that a way to
apply them all atomically.

> The same thing has to be done differently for different platfroms, with some
> new color corrections added, some removed, and some no of coefficients
> changed. I can clearly see a requirement here.

Having them separated into individual properties will make it easy for
userspace to determine at runtime which of them are available and which
aren't. Also it seems to me that all of these properties should have a
unified userspace interface. Drivers would then be free to implement the
kernel side with the hardware-specific details.

> >>AFAIK color management is not a part of atomic modeset, but once we create
> >>such an interface, it would be really easy to club that in the atomic
> >>modeset.
> >
> >See above, this is a reason to _not_ add a separate color manager.
> >-Daniel
> >
> As I mentioned above, color manager is designed to be clubbed with atomic
> modeset, and will not be any blockage there.

I think the point here is that once we have atomic modesetting/pageflip
then there's no longer a need to have an "atomic" color manager
property since there will be a mechanism to atomically apply any number
of properties.

Thierry
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