linux-kernel - Re: [PATCH 03/16] media: rockchip: rga: align stride to 16 bytes

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Message-ID: <2dc6c675-9c69-40a1-b2ed-ff1d22157228@pengutronix.de>
Date: Tue, 2 Dec 2025 15:36:33 +0100
From: Sven Püschel <s.pueschel@...gutronix.de>
To: Nicolas Dufresne <nicolas@...fresne.ca>,
 Jacob Chen <jacob-chen@...wrt.com>,
 Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Heiko Stuebner
 <heiko@...ech.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, kernel@...gutronix.de,
 linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 03/16] media: rockchip: rga: align stride to 16 bytes

Hi Nicolas,

On 10/7/25 8:19 PM, Nicolas Dufresne wrote:
> Hi,
>
>
> Le mardi 07 octobre 2025 à 10:31 +0200, Sven Püschel a écrit :
>> Align the stride to a multiple of 16 according to the RGA3 requirements
>> mentioned in the datasheet. This also ensures that the stride of the RGA2
>> is aligned to 4 bytes, as it needs to divide the value by 4 (one word)
>> before storing it in the register.
>>
>> Increasing the stride for the alignment also requires to increase the
>> sizeimage value. This is usually handled by v4l2_fill_pixfmt_mp, but
>> it doesn't allow to set a stride alignment. Therefore use the generated
>> values to calculate the total number of lines to properly update the
>> sizeimage value after the bytesperline has been aligned.
>>
>> Signed-off-by: Sven Püschel <s.pueschel@...gutronix.de>
>> ---
>>   drivers/media/platform/rockchip/rga/rga.c | 21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
>>
>> diff --git a/drivers/media/platform/rockchip/rga/rga.c
>> b/drivers/media/platform/rockchip/rga/rga.c
>> index
>> 6438119a6c7aeff1e89e7aa95dcd5d2921fefa08..3cb7ce470c47e39d694e8176875a75fad271
>> 7f96 100644
>> --- a/drivers/media/platform/rockchip/rga/rga.c
>> +++ b/drivers/media/platform/rockchip/rga/rga.c
>> @@ -459,6 +459,25 @@ static int vidioc_enum_fmt(struct file *file, void *priv,
>> struct v4l2_fmtdesc *f
>>   	return 0;
>>   }
>>   
>> +static void align_pixfmt(struct v4l2_pix_format_mplane *pix_fmt)
>> +{
>> +	int lines;
>> +	struct v4l2_plane_pix_format *fmt;
>> +
>> +	/*
>> +	 * Align stride to 16 for the RGA3 (based on the datasheet)
>> +	 * To not dismiss the v4l2_fill_pixfmt_mp helper
>> +	 * (and manually write it again), we're approximating the new
>> sizeimage
>> +	 */
>> +	for (fmt = pix_fmt->plane_fmt;
>> +	     fmt < pix_fmt->plane_fmt + pix_fmt->num_planes;
>> +	     fmt++) {
>> +		lines = DIV_ROUND_UP(fmt->sizeimage, fmt->bytesperline);
>> +		fmt->bytesperline = (fmt->bytesperline + 0xf) & ~0xf;
>> +		fmt->sizeimage = fmt->bytesperline * lines;
> Instead of open coding this, describe this with struct v4l2_frmsize_stepwise and
> then use v4l2_apply_frmsize_constraints().
Looking into v4l2_frmsize_stepwise, it only applies to the width/height 
values, whereas I'm interested to control the stride 
byte-alignment/stepping (allowing free range widths/heights).

Do you intent that I (mis)use it like this: 
v4l2_apply_frmsize_constraints(&fmt->bytesperline, &lines, &constraints)  ?

This only replaces one of the three lines in the for loop (where i 
manually do the alignment with & ~0xf) and would also look odd, as i use 
a value in bytes as a width parameter (expected to be in pixels).

Technically the core problem is that the v4l2_fill_pixfmt_mp helper 
doesn't allow to specify a stride byte alignment and just aligns the 
stride based on the format requirements. Therefore I think that maybe 
creating a new v4l2_fill_pixfmt_mp_aligned helper would probably be the 
better solution to get the correct bytesperline value right from the 
start instead of adjusting it afterwards.

Sincerely
     Sven
>
> Nicolas
>
>> +	}
>> +}
>> +
>>   static int vidioc_g_fmt(struct file *file, void *priv, struct v4l2_format *f)
>>   {
>>   	struct v4l2_pix_format_mplane *pix_fmt = &f->fmt.pix_mp;
>> @@ -474,6 +493,7 @@ static int vidioc_g_fmt(struct file *file, void *priv,
>> struct v4l2_format *f)
>>   		return PTR_ERR(frm);
>>   
>>   	v4l2_fill_pixfmt_mp(pix_fmt, frm->fmt->fourcc, frm->width, frm-
>>> height);
>> +	align_pixfmt(pix_fmt);
>>   
>>   	pix_fmt->field = V4L2_FIELD_NONE;
>>   	pix_fmt->colorspace = frm->colorspace;
>> @@ -496,6 +516,7 @@ static int vidioc_try_fmt(struct file *file, void *priv,
>> struct v4l2_format *f)
>>   				(u32)MIN_HEIGHT, (u32)MAX_HEIGHT);
>>   
>>   	v4l2_fill_pixfmt_mp(pix_fmt, fmt->fourcc, pix_fmt->width, pix_fmt-
>>> height);
>> +	align_pixfmt(pix_fmt);
>>   	pix_fmt->field = V4L2_FIELD_NONE;
>>   
>>   	return 0;