linux-kernel - Re: [PATCH] drm: Introduce RGB 64-bit 16:16:16:16 float format

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Message-ID: <20171123160638.GW10981@intel.com>
Date:   Thu, 23 Nov 2017 18:06:38 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Tina Zhang <tina.zhang@...el.com>
Cc:     alex.williamson@...hat.com, kraxel@...hat.com,
        chris@...is-wilson.co.uk, joonas.lahtinen@...ux.intel.com,
        zhenyuw@...ux.intel.com, zhiyuan.lv@...el.com,
        zhi.a.wang@...el.com, kevin.tian@...el.com, daniel@...ll.ch,
        hang.yuan@...el.com, intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH] drm: Introduce RGB 64-bit 16:16:16:16 float format

On Thu, Nov 23, 2017 at 04:56:56PM +0800, Tina Zhang wrote:
> The RGB 64-bit 16:16:16:16 float pixel format is needed by some Apps in
> windows. The float format in each component is 1:5:10 MSb-sign:exponent:
> fraction.
> 
> This patch is to introduce the format to drm, so that the windows guest's
> framebuffer in this kind of format can be recognized and used by linux
> host.
> 
> v14:
> - add some details about the float pixel format. (Daniel)
> - add F suffix to the defined name. (Daniel)
> 
> v12:
> - send to dri-devel at lists.freedesktop.org. (Ville)
> 
> v9:
> - separated from framebuffer decoder patch. (Zhenyu) (Xiaoguang)
> 
> Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Cc: Dave Airlie <airlied@...hat.com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> ---
>  include/uapi/drm/drm_fourcc.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> index 3ad838d..391d2e6 100644
> --- a/include/uapi/drm/drm_fourcc.h
> +++ b/include/uapi/drm/drm_fourcc.h
> @@ -113,6 +113,10 @@ extern "C" {
>  
>  #define DRM_FORMAT_AYUV		fourcc_code('A', 'Y', 'U', 'V') /* [31:0] A:Y:Cb:Cr 8:8:8:8 little endian */
>  
> +/* 64 bpp RGB 16:16:16:16 Floating Point */

As before this is still extremely vague. Stating that each component is
a IEEE-754 half-precision float (binary16) should cover it. Well, assuming
that it really is one.

> +#define DRM_FORMAT_XRGB161616F  fourcc_code('X', 'R', '3', 'F') /* [63:0] x:R:G:B 16:16:16:16 little endian */
> +#define DRM_FORMAT_XBGR161616F  fourcc_code('X', 'B', '3', 'F') /* [63:0] x:B:G:R 16:16:16:16 little endian */

Missing one 16 from that name to be consistent with the non-float stuff.

Also maybe it should be (... '4', 'F')? '3' would seem to imply a 48 bit
pixel.

And of course it's still missing the actual implemntation for any driver.

> +
>  /*
>   * 2 plane RGB + A
>   * index 0 = RGB plane, same format as the corresponding non _A8 format has
> -- 
> 2.7.4

-- 
Ville Syrjälä
Intel OTC