Hello Svyatoslav,
On Thu Oct 2, 2025 at 8:20 AM CEST, Svyatoslav Ryhel wrote:
>> > > > 12 represents amount of bits used per pixel, 8 for Y plane, 2 for U
>> > > > plane and 2 for V plane, total is 12. "but explainable with a comment
>> > > > and improve-able later" why then we cannot use 12 with a comment? this
>> > > > is all arbitrary. Downstream is not wrong from this perspective, you
>> > > > don't take into account that YUV420 is planar and it uses 3 planes a
>> > > > whole Y plane and 1/4 of U and V which in total results in wigth + 2 *
>> > > > 1/4 width which is width * 3/2
>> > >
>> > > Yes -- but AIUI, the only thing the bpp value is used for the
>> > > bytesperline calculation. When we add the special case for planar
>> > > formats, which doesn't use the bpp value, then the value 12 is never
>> > > used anywhere. We should at least have a comment saying it is unused.
>> > > (At that point, we could just hardcode the bpp values in the fmt_align
>> > > function -- but I don't mind either way.)
>> > >
>> > https://ffmpeg.org/pipermail/ffmpeg-user/2023-June/056488.html
>>
>> I understand very well that for YUV420, each pixel has 12 bits of color
>> information. But how many bits of color information each pixel has is not
>> useful in the context of this driver. The number of bytes per line is not
>> related to how many bits of color information each pixel has for planar
>> formats.
>
> No, it has direct impact. This is how buffer size / image size is
> calculated since we place each plane consecutive. And bytes per line
> is used specifically in image size calculation. This is common part
> with non-planar formats. Then since Tegra provides a dedicated
> channels/buffers for each plane, configuration of planar format
> includes an additional step with calculation for each plane.
Sorry, I haven't followed the discussion in detail, but I tested you series
on Tegra20 VIP and capture does not work, with a SIGSEGV in
gstreamer. Bisecting pointed to this as the first commit where the issue
happens.
I compared the input and output values of tegra20_fmt_align() at this
commit and at the previous one, and this is the result:
before this patch with this patch
At function entry:
bpp 1 12
pix->width 640 640
pix->height 480 480
On return:
pix->bytesperline 640 960
pix->sizeimage 460800 460800
I hope these info will help.
Best regards,
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
