On Thu, 20 Jan 2022 at 12:48, Simon Ser <contact@xxxxxxxxxxx> wrote: > Follow-up for the DRM_IOCTL_MODE_GETFB2 docs. Yeah, thanks a lot for doing this, it's really awesome. <3 > +/** > + * struct drm_mode_fb_cmd2 - Frame-buffer metadata. > + * > + * This struct holds frame-buffer metadata. There are two ways to use it: > + * > + * - User-space can fill this struct and perform an &DRM_IOCTL_MODE_ADDFB2 > + * ioctl to register a new frame-buffer. The new frame-buffer object ID will > + * be set by the kernel in @fb_id. > + * - User-space can set @fb_id and perform a &DRM_IOCTL_MODE_GETFB2 ioctl to > + * fetch metadata about an existing frame-buffer. > + * > + * In case of planar formats, this struct allows up to 4 buffer objects with > + * offsets and pitches per plane. The pitch and offset order is dictated by the > + * fourcc, e.g. NV12 (https://fourcc.org/yuv.php#NV12) is described as: > + * > + * YUV 4:2:0 image with a plane of 8 bit Y samples followed by an > + * interleaved U/V plane containing 8 bit 2x2 subsampled colour difference > + * samples. > + * > + * So it would consist of Y as ``offsets[0]`` and UV as ``offsets[1]``. Note > + * that ``offsets[0]`` will generally be 0 (but this is not required). I think the note about offsets[0] usually being zero should be dropped. Equally, rather than referring to fourcc.org, why don't we just refer to drm_fourcc.h and maybe note in there that fourcc.org can be helpful for some formats, but others are missing or mismatching. > + /** > + * @handles: GEM buffer handle, one per plane. Set to 0 if the plane is > + * unused. > */ > __u32 handles[4]; > - __u32 pitches[4]; /* pitch for each plane */ > - __u32 offsets[4]; /* offset of each plane */ > - __u64 modifier[4]; /* ie, tiling, compress */ > + /** @pitches: Pitch (aka. stride), one per plane. */ > + __u32 pitches[4]; > + /** @offsets: Offset into the buffer, one per plane. */ > + __u32 offsets[4]; > + /** > + * @modifier: Format modifier, one per plane. See ``DRM_FORMAT_MOD_*`` > + * constants in ``drm_fourcc.h``. All planes must use the same > + * modifier. Ignored unless &DRM_MODE_FB_MODIFIERS is set in @flags. > + */ > + __u64 modifier[4]; All these fields MBZ (not INVALID!) if the plane is unused. Cheers, Daniel
