Messages in this thread | | | Date | Thu, 12 Jul 2018 18:38:21 +0200 | From | Maxime Ripard <> | Subject | Re: [PATCH 1/9] CHROMIUM: v4l: Add H264 low-level decoder API compound controls. |
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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?
> > > + __s32 offset_for_non_ref_pic; > > + __s32 offset_for_top_to_bottom_field; > > + __u8 num_ref_frames_in_pic_order_cnt_cycle; > > + __s32 offset_for_ref_frame[255]; > > Perhaps use a define instead of hardcoding 255? Not sure if that makes sense. > Same for other arrays below. > > > + __u8 max_num_ref_frames; > > + __u16 pic_width_in_mbs_minus1; > > + __u16 pic_height_in_map_units_minus1; > > + __u8 flags; > > +}; > > You have to test the struct layout for 32 bit and 64 bit systems > (the latter for both 64 bit arm and Intel). The layout should be the > same for all of them since the control framework does not support > compat32 conversions for compound controls.
I'm not really sure how to test that though? Should I write a program doing a bunch of offset_of calls to make sure it matches by hand, or is there anything smarter?
Thanks! Maxime
-- Maxime Ripard, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com
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