linux-kernel - Re: [PATCH 1/9] CHROMIUM: v4l: Add H264 low-level decoder API compound controls.

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Date:   Thu, 12 Jul 2018 18:47:27 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        linux-arm-kernel@...ts.infradead.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        acourbot@...omium.org, jenskuske@...il.com,
        linux-sunxi@...glegroups.com, linux-kernel@...r.kernel.org,
        tfiga@...omium.org,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>, hans.verkuil@...co.com,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        sakari.ailus@...ux.intel.com, Guenter Roeck <groeck@...omium.org>,
        nicolas.dufresne@...labora.com, posciak@...omium.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH 1/9] CHROMIUM: v4l: Add H264 low-level decoder API
 compound controls.

On Thu, Jul 12, 2018 at 06:38:21PM +0200, Maxime Ripard wrote:
> Hi Hans,
> 
> Thanks for your feedback, I have a few things I'm not really sure
> about though.
> 
> On Fri, Jun 15, 2018 at 01:59:58PM +0200, Hans Verkuil wrote:
> > > +struct v4l2_ctrl_h264_sps {
> > > +	__u8 profile_idc;
> > > +	__u8 constraint_set_flags;
> > > +	__u8 level_idc;
> > > +	__u8 seq_parameter_set_id;
> > > +	__u8 chroma_format_idc;
> > > +	__u8 bit_depth_luma_minus8;
> > > +	__u8 bit_depth_chroma_minus8;
> > > +	__u8 log2_max_frame_num_minus4;
> > > +	__u8 pic_order_cnt_type;
> > > +	__u8 log2_max_pic_order_cnt_lsb_minus4;
> > 
> > There is a hole in the struct here. Is that OK? Are there alignment
> > requirements?
> 
> This structure represents an equivalent structure in the H264
> bitstream, but it's not a 1:1 mapping, so I don't think there's any
> alignment issues.
> 
> As of the padding, is it an issue? Isn't it defined by the ABI, and
> therefore the userspace will have the same padding rules?

Hi Maxime

It gets interesting when you have a 64 bit kernel and a 32 bit userspace.

   Andrew