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

[Hans Verkuil]

On 10/22/19 3:17 PM, Paul Kocialkowski wrote:
> 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.

Shouldn't that be a (u32) cast? Since this is used with 32 bit registers?

Regards,

	Hans

> 
> 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
> 
> 
>