Re: [PATCH 0/9] Enhance pipe color support for multi segmented luts

From: Pekka Paalanen <ppaalanen@gmail.com>
To: Harry Wentland <harry.wentland@amd.com>
Cc: intel-gfx@lists.freedesktop.org,
	Uma Shankar <uma.shankar@intel.com>,
	Sebastian Wick <sebastian@sebastianwick.net>,
	dri-devel@lists.freedesktop.org, bhanuprakash.modem@intel.com
Subject: Re: [PATCH 0/9] Enhance pipe color support for multi segmented luts
Date: Mon, 7 Jun 2021 10:29:43 +0300	[thread overview]
Message-ID: <20210607102943.5c9bceb9@eldfell> (raw)
In-Reply-To: <0909131c-1340-c93b-7b80-b661497ccf73@amd.com>

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On Fri, 4 Jun 2021 14:51:25 -0400
Harry Wentland <harry.wentland@amd.com> wrote:

> On 2021-06-01 6:41 a.m., Uma Shankar wrote:
> > Modern hardwares have multi segmented lut approach to prioritize
> > the darker regions of the spectrum. This series introduces a new
> > UAPI to define the lut ranges supported by the respective hardware.
> > 
> > This also enables Pipe Color Management Support for Intel's XE_LPD hw.
> > Enable Support for Pipe Degamma with the increased lut samples
> > supported by hardware. This also adds support for newly introduced
> > Logarithmic Gamma for XE_LPD. Also added the gamma readout support.
> > 
> > The Logarithmic gamma implementation on XE_LPD is non linear and adds 25
> > segments with non linear lut samples in each segment. The expectation
> > is userspace will create the luts as per this distribution and pass
> > the final samples to driver to be programmed in hardware.
> >   
> 
> Is this design targetting Intel XE_LPD HW in particular or is it intended
> to be generic?
> 
> If this is intended to be generic I think it would benefit from a lot more
> documentation. At this point it's difficult for me to see how to adapt this
> to AMD HW. It would take me a while to be comfortable to make a call on whether
> we can use it or not. And what about other vendors?
> 
> I think we need to be cautious in directly exposing HW functionality through
> UAPI. The CM parts of AMD HW seem to be changing in some way each generation
> and it looks like the same is true for Intel. The trouble we have with adapting
> the old gamma/degamma properties to modern HW is some indication to me that
> this approach is somewhat problematic.
> 
> It would be useful to understand and document the specific use-cases we want to
> provide to userspace implementers with this functionality. Do we want to support
> modern transfer functions such as PQ or HLG? If so, it might be beneficial to
> have an API to explicitly specify that, and then use LUT tables in drivers that
> are optimized for the implementing HW.

Hi Harry,

from my very limited understanding so far, enum might be fine for PQ,
but HLG is not just one transfer function, although it may often be
confused as one. PQ and HLG are fundamentally different designs to HDR
broadcasting I believe. It would be unfortunate to make a mistake here,
engraving it into UAPI.

> Or is the use case tone mapping? If so,
> would a parametric definition of tone mapping be easier to manage?

A very good question at least I have no idea about.

Thanks,
pq

> > +-----+------------------------------+
> > | x   |  2 pow x segment|No of Entries
> > |     |  0              | 1          |
> > | 0   |  1              | 1          |
> > | 1   |  2              | 2          |
> > | 2   |  4              | 2          |
> > | 3   |  8              | 2          |
> > | 4   |  16             | 2          |
> > | 5   |  32             | 4          |
> > | 6   |  64             | 4          |
> > | 7   |  128            | 4          |
> > | 8   |  256            | 8          |
> > | 9   |  512            | 8          |
> > | 10  |  1024           | 8          |
> > | 11  |  2048           | 16         |
> > | 12  |  4096           | 16         |
> > | 13  |  8192           | 16         |
> > | 14  |  16384          | 32         |
> > | 15  |  32768          | 32         |
> > | 16  |  65536          | 64         |
> > | 17  |  131072         | 64         |
> > | 18  |  262144         | 64         |
> > | 19  |  524288         | 32         |
> > | 20  |  1048576        | 32         |
> > | 21  |  2097152        | 32         |
> > | 22  |  4194304        | 32         |
> > | 23  |  8388608        | 32         |
> > | 24  |  16777216       | 1          |
> > |     | Total Entries   | 511        |
> >  -----+-----------------+------------+
> > 
> > Credits: Special mention and credits to Ville Syrjala for coming up
> > with a design for this feature and inputs. This series is based on
> > his original design.
> > 
> > Note: Userspace support for this new UAPI will be done on Chrome and
> > plan is to get this supported on mutter as well. We will notify the
> > list once we have that ready for review.
> >   
> 
> Is this an RFC? If so it would be good to mark it as such.
> 
> Harry
> 
> > Uma Shankar (9):
> >   drm: Add gamma mode property
> >   drm/i915/xelpd: Define color lut range structure
> >   drm/i915/xelpd: Add support for Logarithmic gamma mode
> >   drm/i915/xelpd: Attach gamma mode property
> >   drm: Add Client Cap for advance gamma mode
> >   drm/i915/xelpd: logarithmic gamma enabled only with advance gamma mode
> >   drm/i915/xelpd: Enable Pipe Degamma
> >   drm/i915/xelpd: Add Pipe Color Lut caps to platform config
> >   drm/i915/xelpd: Enable XE_LPD Gamma Lut readout
> > 
> >  drivers/gpu/drm/drm_atomic_uapi.c          |   8 +
> >  drivers/gpu/drm/drm_color_mgmt.c           |  75 ++++
> >  drivers/gpu/drm/drm_ioctl.c                |   5 +
> >  drivers/gpu/drm/i915/display/intel_color.c | 454 ++++++++++++++++++++-
> >  drivers/gpu/drm/i915/i915_pci.c            |   3 +-
> >  drivers/gpu/drm/i915/i915_reg.h            |   7 +
> >  include/drm/drm_atomic.h                   |   1 +
> >  include/drm/drm_color_mgmt.h               |   8 +
> >  include/drm/drm_crtc.h                     |  25 ++
> >  include/drm/drm_file.h                     |   8 +
> >  include/uapi/drm/drm.h                     |   8 +
> >  include/uapi/drm/drm_mode.h                |  43 ++
> >  12 files changed, 630 insertions(+), 15 deletions(-)
> >   
> 

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