linux-kernel - [PATCH 0/1] [RFC] drm/fourcc: Add new unsigned R16_UINT/RG1616

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Date:   Mon, 27 Jun 2022 13:40:04 +0000
From:   Dennis Tsiang <Dennis.Tsiang@....com>
To:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
CC:     "maarten.lankhorst@...ux.intel.com" 
        <maarten.lankhorst@...ux.intel.com>,
        "mripard@...nel.org" <mripard@...nel.org>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        Liviu Dudau <Liviu.Dudau@....com>,
        Brian Starkey <Brian.Starkey@....com>,
        Lisa Wu <lisa.wu@....com>,
        Normunds Rieksts <Normunds.Rieksts@....com>,
        Dennis Tsiang <Dennis.Tsiang@....com>, nd <nd@....com>
Subject: [PATCH 0/1] [RFC] drm/fourcc: Add new unsigned R16_UINT/RG1616_UINT
 formats

This patch is an early RFC to discuss the viable options and
alternatives for inclusion of unsigned integer formats for the DRM API.

This patch adds a new single component 16-bit and a two component 32-bit
DRM fourcc’s that represent unsigned integer formats. The use case for
needing UINT formats, in our case, would be to support using raw buffers
for camera ISPs.

For images imported with DRM fourcc + modifier combination, the GPU
driver needs a way to determine the datatype of the format which
currently the DRM API does not provide explicitly with a notable
exception of the floating-point fourccs such as DRM_FORMAT_XRGB16161616F
as an example. As the DRM fourccs do not currently define the
interpretation of the data, should the information be made explicit in
the DRM API similarly to how it is already done in Vulkan?

The reason for introducing datatype to the DRM fourcc's is that the
alternative, for any API (e.g., EGL) that lacks the format datatype
information for fourcc/modifier combination for dma_buf interop would be
to introduce explicit additional metadata/attributes that encode this
information which then would be passed to the GPU driver but the
drawback of this is that it would require extending multiple graphics
APIs to support every single platform.

By having the DRM API expose the datatype information for formats saves
a lot of integration/verification work for all of the different graphics
APIs and platforms as this information could be determined by the DRM
triple alone for dma_buf interop.

It would be good to gather some opinions on what others think about
introducing datatypes to the DRM API.

Any feedback and suggestions are highly appreciated.

Dennis Tsiang (1):
  [RFC] drm/fourcc: Add new unsigned R16_UINT/RG1616_UINT formats

 include/uapi/drm/drm_fourcc.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--
2.36.1

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