[PATCH] drm/color: Include CTM equations in kerneldoc

[Daniel Vetter]

On Fri, Jan 27, 2017 at 04:13:42PM +0200, Ville Syrjälä wrote:
> On Fri, Jan 27, 2017 at 01:50:19PM +0000, Brian Starkey wrote:
> > On Fri, Jan 27, 2017 at 03:27:09PM +0200, Ville Syrjälä wrote:
> > >On Fri, Jan 27, 2017 at 10:47:48AM +0000, Brian Starkey wrote:
> > >> Explicitly state the expected CTM equations in the kerneldoc for the CTM
> > >> property.
> > >>
> > >> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > >> Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> > >> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > >> Signed-off-by: Brian Starkey <brian.starkey at arm.com>
> > >> ---
> > >>
> > >> Hi,
> > >>
> > >> This captures the outcome of the discussion on #dri-devel yesterday
> > >> (2017-01-26):
> > >> https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2017-01-26
> > >>
> > >> I'm not sure about the stance on such explicit rst markup in kerneldoc,
> > >> but without it the equations are pretty unreadable in the rendered
> > >> output.
> > >>
> > >> Cheers,
> > >> Brian
> > >>
> > >>  drivers/gpu/drm/drm_color_mgmt.c |   10 ++++++++++
> > >>  1 file changed, 10 insertions(+)
> > >>
> > >> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> > >> index 789b4c65cd69..63f3a7404fa1 100644
> > >> --- a/drivers/gpu/drm/drm_color_mgmt.c
> > >> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> > >> @@ -62,6 +62,16 @@
> > >>   *	unit/pass-thru matrix should be used. This is generally the driver
> > >>   *	boot-up state too.
> > >>   *
> > >> + *	Given an input vector ``in[3]`` and an output vector ``out[3]``, the
> > >> + *	transformation applied is:
> > >> + *
> > >> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
> > >> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
> > >> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
> > >> + *
> > >> + *	| For RGB formats, the input vector is assumed to be ``{ R, G, B }``.
> > >> + *	| For YCbCr formats, the input vector is assumed to be ``{ Y, Cb, Cr }``.
> > >
> > >Talking about formats here could be a little confusing. One might think
> > >this has something to do with the framebuffer pixel format, when in fact
> > >it's only about the internal format used by the crtc.
> > 
> > Ah right, yes I see.
> > 
> > Actually, I *was* thinking about the framebuffer format here - but
> > that is missing the context of us adding a CTM property for each plane
> > (so that each plane can map the framebuffer format to the CRTC pipe's
> > internal format).
> > 
> > Our intention (for Mali-DP) is to add CTM on each plane to be used
> > for framebuffer -> CRTC pipe conversion, and then use the CTM on the
> > CRTC for CRTC pipe -> output conversion.
> > 
> > Shall I just remove the two lines about pixel formats here, and then
> > when we land per-plane CTM add some details about plane CTM matrices
> > being before the CRTC CTM matrix?
> 
> We'll need to keep some note about the RGB order here. Userspace needs
> to know that to actually use the matrix. Oh and I guess we should really
> put this documentation into the uapi header.

Atm properties are documented in kernel-doc since they don't exist at all
in the uapi. Well this here is somewhat an exception, since there's
structs in uapi. But since nothing else in uapi thus far is reasonably
documented I still think we should keep it in the kernel-doc for now. At
least until someone starts taggling uapi docs properly ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch