linux-kernel - Re: [PATCH v7 02/11] drm/fourcc: Add DRM_FORMAT

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Message-ID: <d8051388-d48d-412b-84d3-55399ce68447@ideasonboard.com>
Date: Wed, 28 Jan 2026 15:53:21 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Vishal Sagar <vishal.sagar@....com>,
 Anatoliy Klymenko <anatoliy.klymenko@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Michal Simek <michal.simek@....com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Pekka Paalanen <ppaalanen@...il.com>, Dmitry Baryshkov <lumag@...nel.org>
Subject: Re: [PATCH v7 02/11] drm/fourcc: Add DRM_FORMAT_XV15/XV20

Hi,

On 28/01/2026 14:21, Laurent Pinchart wrote:
> Hi Tomi,
> 
> On Mon, Dec 01, 2025 at 02:18:44PM +0200, Tomi Valkeinen wrote:
>> Add two new pixel formats:
>>
>> DRM_FORMAT_XV15 ("XV15")
>> DRM_FORMAT_XV20 ("XV20")
>>
>> The formats are 2 plane 10 bit per component YCbCr, with the XV15 2x2
>> subsampled whereas XV20 is 2x1 subsampled.
>>
>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> Reviewed-by: Vishal Sagar <vishal.sagar@....com>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> ---
>>  drivers/gpu/drm/drm_fourcc.c  | 6 ++++++
>>  include/uapi/drm/drm_fourcc.h | 8 ++++++++
>>  2 files changed, 14 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
>> index e662aea9d105..b22ef86428a1 100644
>> --- a/drivers/gpu/drm/drm_fourcc.c
>> +++ b/drivers/gpu/drm/drm_fourcc.c
>> @@ -381,6 +381,12 @@ const struct drm_format_info *__drm_format_info(u32 format)
>>  		{ .format = DRM_FORMAT_S416,            .depth = 0,  .num_planes = 3,
>>  		  .char_per_block = { 2, 2, 2 }, .block_w = { 1, 1, 1 }, .block_h = { 1, 1, 1 },
>>  		  .hsub = 1, .vsub = 1, .is_yuv = true},
>> +		{ .format = DRM_FORMAT_XV15,		.depth = 0,  .num_planes = 2,
>> +		  .char_per_block = { 4, 8, 0 }, .block_w = { 3, 3, 0 }, .block_h = { 1, 1, 0 },
>> +		  .hsub = 2, .vsub = 2, .is_yuv = true },
> 
> Given the horizontal subsampling, don't we have 6 pixels in 8 bytes ?

No, the hsub is applied first.

If you look at framebuffer_check() and the called functions, the
calculations for the min_pitch for a 1920 wide XV15 buffer for the
second plane is:

width = frame_width / hsub
min_pitch = width * char_per_block[plane] / block_w[plane]

So:

width = 1920 / 2 = 960
min_pitch = 960 * 8 / 3 = 2560

 Tomi