[PATCH v2 7/7] drm: rcar-du: Add new formats (2-10-10-10 ARGB, Y210)

[Hans Verkuil]

On 20/12/2022 10:09, Geert Uytterhoeven wrote:
> Hi Hans,
> 
> On Tue, Dec 20, 2022 at 10:01 AM Hans Verkuil <hverkuil-cisco at xs4all.nl> wrote:
>> On 19/12/2022 22:47, Laurent Pinchart wrote:
>>> (CC'ing Sakari and Hans)
>>>
>>> Thank you for the patch.
>>>
>>> On Mon, Dec 19, 2022 at 04:01:39PM +0200, Tomi Valkeinen wrote:
>>>> Add new pixel formats: RGBX1010102, RGBA1010102, ARGB2101010 and Y210.
>>>>
>>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas at ideasonboard.com>
>>>> ---
>>>>  drivers/gpu/drm/rcar-du/rcar_du_kms.c | 24 +++++++++++++
>>>>  drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 49 +++++++++++++++++++++++++--
>>>>  2 files changed, 71 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_kms.c b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
>>>> index 8c2719efda2a..8ccabf5a30c4 100644
>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_kms.c
>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
>>>> @@ -259,6 +259,24 @@ static const struct rcar_du_format_info rcar_du_format_infos[] = {
>>>>              .bpp = 32,
>>>>              .planes = 1,
>>>>              .hsub = 1,
>>>> +    }, {
>>>> +            .fourcc = DRM_FORMAT_RGBX1010102,
>>>
>>> Ah, here the format makes sense.
>>>
>>>> +            .v4l2 = V4L2_PIX_FMT_XBGR2101010,
>>>
>>> But this is horrible :-( Could we use the same names as DRM for new
>>> formats, when there is no conflict with existing V4L2 formats ?
>>>
>>> Sakari, Hans, what do you think ? Please see patch 1/7 in the series for
>>> the format definitions.
>>
>> V4L2 describes pixel formats based on how they appear in memory from the
>> lowest to highest memory address.
> 
> So that means big endian?

Yes.

> 
>> If I am not mistaken, DRM uses the CPU order. So that explains the difference
>> in naming. I don't think we should hide that difference. And V4L2 has been
>> quite consistent in following memory ordering in the naming (except possibly
>> for some of the really old pixelformats).
> 
> DRM uses little endian.

So not CPU order, but always little endian order? I.e., on a big endian system
a given DRM_FORMAT_ would have the same memory layout as on a little endian
system?

Regards,

	Hans

> 
>> Departing from that would be more of a hindrance than a help, IMHO.
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds