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Date: Tue, 21 Aug 2018 18:09:40 +0100 From: Alexandru-Cosmin Gheorghe <Alexandru-Cosmin.Gheorghe@....com> To: Brian Starkey <brian.starkey@....com>, dri-devel@...ts.freedesktop.org, airlied@...ux.ie, gustavo@...ovan.org, maarten.lankhorst@...ux.intel.com, seanpaul@...omium.org, corbet@....net, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, liviu.dudau@....com, ayan.halder@....com Cc: nd@....com Subject: Re: [PATCH] drm/fourcc: Add DOC: overview comment On Tue, Aug 21, 2018 at 06:51:26PM +0200, Daniel Vetter wrote: > 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@...ll.ch> > > Signed-off-by: Brian Starkey <brian.starkey@....com> > > --- > > 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@...ll.ch> > > I'll leave pushing to one of the arm committers for drm-misc. > -Daniel Done. > > > + * 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 -- Cheers, Alex G
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