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

From: Mauro Carvalho Chehab <mchehab@kernel.org>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: Nicolas Dufresne <nicolas@ndufresne.ca>,
	Jernej Skrabec <jernej.skrabec@siol.net>,
	Jonas Karlman <jonas@kwiboo.se>, Chen-Yu Tsai <wens@csie.org>,
	Maxime Ripard <mripard@bootlin.com>,
	linux-kernel@vger.kernel.org, Hans Verkuil <hverkuil@xs4all.nl>,
	linux-sunxi@googlegroups.com,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Tomasz Figa <tfiga@chromium.org>,
	Ezequiel Garcia <ezequiel@collabora.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v8 3/3] media: cedrus: Add HEVC/H.265 decoding support
Date: Thu, 17 Oct 2019 09:57:51 -0300	[thread overview]
Message-ID: <20191017095751.5a229051@coco.lan> (raw)
In-Reply-To: <20190927143411.141526-4-paul.kocialkowski@bootlin.com>

Em Fri, 27 Sep 2019 16:34:11 +0200
Paul Kocialkowski <paul.kocialkowski@bootlin.com> 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@bootlin.com>
> ---

...

> +		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.

> +#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.

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.

Thanks,
Mauro

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