Re: [PATCH v8 3/3] media: cedrus: Add HEVC/H.265 decoding support

[Paul Kocialkowski]

Hi again,

On Tue 22 Oct 19, 14:40, Paul Kocialkowski wrote:
> Hi Mauro and thanks for the review,
> 
> On Thu 17 Oct 19, 09:57, Mauro Carvalho Chehab wrote:
> > Em Fri, 27 Sep 2019 16:34:11 +0200
> > Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> escreveu:
> > 
> > > This introduces support for HEVC/H.265 to the Cedrus VPU driver, with
> > > both uni-directional and bi-directional prediction modes supported.
> > > 
> > > Field-coded (interlaced) pictures, custom quantization matrices and
> > > 10-bit output are not supported at this point.
> > > 
> > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx>
> > > ---
> > 
> > ...
> > 
> > > +		unsigned int ctb_size_luma =
> > > +			1 << log2_max_luma_coding_block_size;
> > 
> > Shifts like this is a little scary. "1" constant is signed. So, if
> > log2_max_luma_coding_block_size is 31, the above logic has undefined
> > behavior. Different archs and C compilers may handle it on different
> > ways.
> 
> I wasn't aware that it was the case, thanks for bringing this to light!
> I'll make it 1UL then.
> 
> > > +#define VE_DEC_H265_LOW_ADDR_PRIMARY_CHROMA(a) \
> > > +	(((a) << 24) & GENMASK(31, 24))
> > 
> > Same applies here and on other similar macros. You need to enforce
> > (a) to be unsigned, as otherwise the behavior is undefined.
> > 
> > Btw, this is a recurrent pattern on this file. I would define a
> > macro, e. g. something like:
> > 
> > 	#define MASK_BITS_AND_SHIFT(v, high, low) \
> > 		((UL(v) << low) & GENMASK(high, low))
> > 
> > And use it for all similar patterns here.
> 
> Sounds good! I find that the reverse wording (SHIFT_AND_MASK_BITS) would be
> a bit more explicit since the shift happens prior to the mask.

Apparently the UL(v) macro just appends UL to v in preprocessor, so it won't
work with anything else than direct integers.

I'll replace it with a (unsigned long) cast, that seems to do the job.

Cheers,

Paul

> Also we probably need to have parenthesis around "low", right?
> 
> > The best would be to include such macro at linux/bits.h, although some
> > upstream discussion is required.
> > 
> > So, for now, let's add it at this header file, but work upstream
> > to have it merged there.
> 
> Understood, I'll include it in that header for now and send a separate patch
> for inclusion in linux/bits.h (apparently the preprocessor doesn't care about
> redefinitions so we can just remove the cedrus fashion once the common one is
> in).
> 
> What do you think?
> 
> Cheers,
> 
> Paul



-- 
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