On Tue, Aug 21, 2018 at 05:16:11PM +0100, Brian Starkey wrote: > There's a number of things which haven't previously been documented > around the usage of format modifiers. Capture the current > understanding in an overview comment and add it to the rst > documentation. > > Ideally, the generated documentation would also include documentation > of all of the #defines, but the kernel-doc system doesn't currently > support kernel-doc comments on #define constants. > > Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > Signed-off-by: Brian Starkey <brian.starkey@xxxxxxx> > --- > Documentation/gpu/drm-kms.rst | 6 ++++++ > include/uapi/drm/drm_fourcc.h | 36 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 42 insertions(+) > > diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst > index 1dffd1ac4cd4..1dd9f4824d3b 100644 > --- a/Documentation/gpu/drm-kms.rst > +++ b/Documentation/gpu/drm-kms.rst > @@ -322,6 +322,12 @@ Frame Buffer Functions Reference > DRM Format Handling > =================== > > +.. kernel-doc:: include/uapi/drm/drm_fourcc.h > + :doc: overview > + > +Format Functions Reference > +-------------------------- > + > .. kernel-doc:: include/drm/drm_fourcc.h > :internal: > > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h > index 894fa2da32fd..3f6c0b499323 100644 > --- a/include/uapi/drm/drm_fourcc.h > +++ b/include/uapi/drm/drm_fourcc.h > @@ -30,6 +30,42 @@ > extern "C" { > #endif > > +/** > + * DOC: overview > + * > + * In the DRM subsystem, framebuffer pixel formats are described using the > + * fourcc codes defined in `include/uapi/drm/drm_fourcc.h`. In addition to the > + * fourcc code, a Format Modifier may optionally be provided, in order to > + * further describe the buffer's format - for example tiling or compression. > + * > + * Format Modifiers > + * ---------------- > + * > + * Format modifiers are used in conjunction with a fourcc code, forming a > + * unique fourcc:modifier pair. This format:modifier pair must fully define the > + * format and data layout of the buffer, and should be the only way to describe > + * that particular buffer. > + * > + * Having multiple fourcc:modifier pairs which describe the same layout should > + * be avoided, as such aliases run the risk of different drivers exposing > + * different names for the same data format, forcing userspace to understand > + * that they are aliases. > + * > + * Format modifiers may change any property of the buffer, including the number > + * of planes and/or the required allocation size. Format modifiers are > + * vendor-namespaced, and as such the relationship between a fourcc code and a > + * modifier is specific to the modifer being used. For example, some modifiers > + * may preserve meaning - such as number of planes - from the fourcc code, > + * whereas others may not. > + * > + * Vendors are encouraged to document their modifier usage in as much detail as I'd go with a slightly stronger "... should document ..." but either way: Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> I'll leave pushing to one of the arm committers for drm-misc. -Daniel > + * possible, to ensure maximum compatibility across devices, drivers and > + * applications. > + * > + * The authoritative list of format modifier codes is found in > + * `include/uapi/drm/drm_fourcc.h` > + */ > + > #define fourcc_code(a, b, c, d) ((__u32)(a) | ((__u32)(b) << 8) | \ > ((__u32)(c) << 16) | ((__u32)(d) << 24)) > > -- > 2.16.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch