Re: [PATCH v7 2/4] media: rockchip: Add JPEG decoder driver

[Sergei Khomenkov <shomenkow@gmail.com>]

Hi Sascha,

> +/* Bytes per pixel used to size a coded buffer for a given resolution. */
> +#define RKJPEGD_CODED_MAX_DEPTH	2

A valid JPEG can be larger than 2 bytes per pixel. libjpeg-turbo sizes
its worst case in tj3JPEGBufSize() at 3 bytes per pixel for 4:2:0, 4
for 4:2:2 and 6 for 4:4:4, plus 2 KiB. Quality 100 noise comes close:
2.75 bytes per pixel at 4:2:0, both from libjpeg and from the Hantro H1
encoder on an RK3026. Such a frame does not fit the default buffer; by
your commit message a truncated one fails through BUF_EMPTY, so the
client gets an ERROR buffer for a valid picture. I can't run the VDPU720
to confirm.

The default only matters to clients that pass sizeimage 0. GStreamer
1.26 asks for max_width * max_height / 2 of the enumerated range; at
65528x65528 that wraps in its 32-bit calculate_max_sizeimage() to about
255 MiB, which the driver keeps, so 1.26 is not affected. Its main
branch (08ea5bc9fab9) asks for width * height bytes of the stream,
which the driver keeps too, so these frames would not fit. Both are
from reading the code; I did not run them on this driver.

Would 3 bytes per pixel be acceptable as the default, and as a floor
for smaller requests, like the 2 bytes per pixel floor in 6/7 of your
hantro-based v1? 4:4:4 at quality 100 would still not fit, but the
subsampling is not known before the header is parsed.

Thanks,
Sergei