Hello, On Fri, 08 Oct 2021 14:19:41 +0200 Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote: > Hi Dorota, > > On Wed, 2021-10-06 at 13:05 +0200, Dorota Czaplejewicz wrote: > > Section 13.7.6.13 "CSI Image Parameter Register" of the > > i.MX 8M Quad Applications Processors Reference Manual > > states that the line size should be divisible by 8 bytes. > > However, the hardware also accepts sizes divisible by 4 bytes. > > > > This patch accepts line sizes divisible 4-bytes in non-planar mode. > > Thank you, this makes it much clearer. I see two issues with this, > though, one small and one a bit bigger: > > First, I'd be wary of disregarding the reference manual - unless we know > better, and then it should be well documented in the code. It might be > that the 8-byte alignment requirement stems from the fact that the FIFO > operates in double-word units, which might cause the CSI to write over > the end of the buffer if the line width is odd (in 32-bit words). > Or maybe it's just that the FBUF_STRIDE conflicts with this, I'm unclear > on whether that is only given in units of dwords (although the driver > currently doesn't support this anyway). > > I wonder: if you use 4-byte aligned width and odd height, does the CSI > write over the end of the buffer? I tested this case, and found a glitch which suggests the last 4 bytes are ignored: https://source.puri.sm/Librem5/linux-next/uploads/cfb59e3832431aaa3a69549455502568/image.png That would be taken care of rounding up towards a number decided at runtime, like: divisor = 8 >> (mbus->height % 2); > > > Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@xxxxxxx> > > --- > > > > Hello, > > > > my previous patch identified something that was not a problem, > > so I'm sending a different one. > > > > This has been tested on the Librem 5. > > > > Cheers, > > Dorota > > > > drivers/staging/media/imx/imx-media-utils.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/staging/media/imx/imx-media-utils.c b/drivers/staging/media/imx/imx-media-utils.c > > index 5128915a5d6f..a303003929e3 100644 > > --- a/drivers/staging/media/imx/imx-media-utils.c > > +++ b/drivers/staging/media/imx/imx-media-utils.c > > @@ -545,13 +545,13 @@ int imx_media_mbus_fmt_to_pix_fmt(struct v4l2_pix_format *pix, > > } > > > > /* Round up width for minimum burst size */ > > - width = round_up(mbus->width, 8); > > + width = round_up(mbus->width, 4); > > > > /* Round up stride for IDMAC line start address alignment */ > > if (cc->planar) > > stride = round_up(width, 16); > > else > > - stride = round_up((width * cc->bpp) >> 3, 8); > > + stride = round_up((width * cc->bpp) >> 3, 4); > > Second, even if this works fine on the i.MX7/8M CSI, the alignment is > still required for the i.MX5/6 IPU, for which this code and the comments > were written. So we need a way to differentiate the two cases here. > > regards > Philipp How best to go about this? I can see in the file imx-media-capture.c that there the video device lives in struct capture_priv.vdev.vfd. Would that be the right place to query about the underlying hardware? Then the following functions would gain a new "small_divisor" parameter: - imx_media_mbus_fmt_to_pix_fmt (a GPL symbol) - imx_media_mbus_fmt_to_ipu_image (a GPL symbol) - __capture_try_fmt Those would have to extract the device type from struct capture_priv: - __capture_legacy_try_fmt - capture_try_fmt_vid_cap - capture_s_fmt_vid_cap - capture_init_format Regards, Dorota
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