Re: [PATCH v3 3/4] media: imx: imx7-media-csi: Lift width constraints for 8bpp formats

Alexander Stein
2023-04-19T07:02:25Z

Hi Laurent,

thanks for the feedback.

Am Dienstag, 18. April 2023, 17:59:47 CEST schrieb Laurent Pinchart:
> Hi Alexander,
>
> Thank you for the patch.
>
> The commit message should state "Lift width constraint for 16bpp
> formats".

To be pedantic it should be called "Lift width constraint for non-8bpp
formats" :)

> I would also phrase is "Relax" instead of "Lift" as it's not
> completely lifted.

That's true, this subtle difference should be accounted for. Thanks.

> On Tue, Apr 18, 2023 at 02:20:40PM +0200, Alexander Stein wrote:
> > For 8-bit formats the image_width just needs to be a multiple of 8 pixels
> > others just a multiple of 4 pixels.
>
> This is a bit terse, and I think a word or two are missing. It could be
> improved:
>
> The driver unconditionally aligns the image width to multiples of 8
> pixels. The real alignment constraint is 8 bytes, as indicated by the
> CSI_IMAG_PARA.IMAGE_WIDTH documentation that calls for 8 pixel alignment
> for 8bpp formats and 4 pixel alignment for other formats.

Thanks for this suggestion. This sounds much better.

> > Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> > ---
> > Changes in v3:
> > * Fix commit message (Only 8-bit formats needs multiple of 8 pixels)
> >
> > drivers/media/platform/nxp/imx7-media-csi.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/platform/nxp/imx7-media-csi.c
> > b/drivers/media/platform/nxp/imx7-media-csi.c index
> > 1315f5743b76f..730c9c57bf4bc 100644
> > --- a/drivers/media/platform/nxp/imx7-media-csi.c
> > +++ b/drivers/media/platform/nxp/imx7-media-csi.c
> > @@ -1146,6 +1146,7 @@ __imx7_csi_video_try_fmt(struct v4l2_pix_format
> > *pixfmt,>
> > struct v4l2_rect *compose)
> >
> > {
> >
> > const struct imx7_csi_pixfmt *cc;
> >
> > + u32 walign;
> >
> > if (compose) {
> >
> > compose->width = pixfmt->width;
> >
> > @@ -1162,13 +1163,19 @@ __imx7_csi_video_try_fmt(struct v4l2_pix_format
> > *pixfmt,>
> > cc = imx7_csi_find_pixel_format(pixfmt->pixelformat);
> >
> > }
> >
> > + /* Refer to CSI_IMAG_PARA.IMAGE_WIDTH description */
> > + if (cc->bpp == 8)
> > + walign = 8;
> > + else
> > + walign = 4;
>
> Would the following convey the purpose better ?
>
> /*
> * The width alignment is 8 bytes as indicated by the
> * CSI_IMAG_PARA.IMAGE_WIDTH documentation. Convert it to pixels.
> */
> walign = 8 * 8 / cc->bpp;

I was wondering how to shorten this calculation without using ? operator,
nice.

> > +
> >
> > /*
> >
> > * Round up width for minimum burst size.
> > *
> > * TODO: Implement configurable stride support, and check what the
real
> > * hardware alignment constraint on the width is.
> > */
>
> We can now drop the second part of the sentence :-) The first line is
> actually not very accurate anymore. How about
>
> /*
> * The width alignment is 8 bytes as indicated by the
> * CSI_IMAG_PARA.IMAGE_WIDTH documentation. Convert it to pixels.
> *
> * TODO: Implement configurable stride support.
> */
> walign = 8 * 8 / cc->bpp;
> v4l_bound_align_image(&pixfmt->width, 1, 0xffff, walign,
> &pixfmt->height, 1, 0xffff, 1, 0);

That's neat, thanks. I'll update accordingly.

Best regards,
Alexander

> > - v4l_bound_align_image(&pixfmt->width, 1, 0xffff, 8,
> > + v4l_bound_align_image(&pixfmt->width, 1, 0xffff, walign,
> >
> > &pixfmt->height, 1, 0xffff, 1, 0);
> >
> > pixfmt->bytesperline = pixfmt->width * cc->bpp / 8;

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