linux-kernel - Re: [PATCH v5 01/14] media: ti: j721e-csi2rx: Remove word size alignment on frame width

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Message-ID: <175707045529.8095.7424566069689990352@freya>
Date: Fri, 05 Sep 2025 16:37:35 +0530
From: Jai Luthra <jai.luthra@...asonboard.com>
To: Rishikesh Donadkar <r-donadkar@...com>, jai.luthra@...ux.dev, laurent.pinchart@...asonboard.com, mripard@...nel.org
Cc: r-donadkar@...com, y-abhilashchandra@...com, devarsht@...com, vaishnav.a@...com, s-jain1@...com, vigneshr@...com, mchehab@...nel.org, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, sakari.ailus@...ux.intel.com, hverkuil-cisco@...all.nl, tomi.valkeinen@...asonboard.com, changhuang.liang@...rfivetech.com, jack.zhu@...rfivetech.com, linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v5 01/14] media: ti: j721e-csi2rx: Remove word size alignment on frame width

Hi Rishikesh,

Quoting Rishikesh Donadkar (2025-08-25 19:55:09)
> j721e-csi2rx driver has a limitation of frame width being a multiple
> word size. However, there is no such limitation imposed by the
> hardware [1].

Is there no limitation for the step size, or also not limitation for the
minimum size of transfer?

> 
> Remove this limitation from the driver.
> 
> Link: https://www.ti.com/lit/pdf/spruj16
> Signed-off-by: Rishikesh Donadkar <r-donadkar@...com>
> ---
>  .../platform/ti/j721e-csi2rx/j721e-csi2rx.c     | 17 +++--------------
>  1 file changed, 3 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> index 3992f8b754b7..b3a27f4c3210 100644
> --- a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> +++ b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> @@ -260,9 +260,6 @@ static void ti_csi2rx_fill_fmt(const struct ti_csi2rx_fmt *csi_fmt,
>                              MAX_WIDTH_BYTES * 8 / csi_fmt->bpp);

Here the pix->width is restricted to be at minimum pixels_in_word.
So TRY_FMT/S_FMT with a width = 1 will be clamped by the driver.

>         pix->height = clamp_t(unsigned int, pix->height, 1, MAX_HEIGHT_LINES);
>  
> -       /* Width should be a multiple of transfer word-size */
> -       pix->width = rounddown(pix->width, pixels_in_word);
> -
>         v4l2_fmt->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
>         pix->pixelformat = csi_fmt->fourcc;
>         pix->bytesperline = pix->width * (csi_fmt->bpp / 8);
> @@ -360,23 +357,15 @@ static int ti_csi2rx_enum_framesizes(struct file *file, void *fh,
>                                      struct v4l2_frmsizeenum *fsize)
>  {
>         const struct ti_csi2rx_fmt *fmt;
> -       unsigned int pixels_in_word;
>  
>         fmt = find_format_by_fourcc(fsize->pixel_format);
>         if (!fmt || fsize->index != 0)
>                 return -EINVAL;
>  
> -       /*
> -        * Number of pixels in one PSI-L word. The transfer happens in multiples
> -        * of PSI-L word sizes.
> -        */
> -       pixels_in_word = PSIL_WORD_SIZE_BYTES * 8 / fmt->bpp;
> -
>         fsize->type = V4L2_FRMSIZE_TYPE_STEPWISE;
> -       fsize->stepwise.min_width = pixels_in_word;
> -       fsize->stepwise.max_width = rounddown(MAX_WIDTH_BYTES * 8 / fmt->bpp,
> -                                             pixels_in_word);
> -       fsize->stepwise.step_width = pixels_in_word;
> +       fsize->stepwise.min_width = 1;

But here, in ENUM_FRAMESIZES we allow width to go as low as 1.

Can you make sure both of them match whatever is correct (and possible by
the hardware)?

> +       fsize->stepwise.max_width = MAX_WIDTH_BYTES * 8 / fmt->bpp;
> +       fsize->stepwise.step_width = 1;
>         fsize->stepwise.min_height = 1;
>         fsize->stepwise.max_height = MAX_HEIGHT_LINES;
>         fsize->stepwise.step_height = 1;
> -- 
> 2.34.1
> 

Thanks,
    Jai