Re: [RFC] drm: Add utility function to check for edp1.4

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Oct 29, 2014 at 02:42:29PM +0100, Thierry Reding wrote:
> On Wed, Oct 22, 2014 at 11:45:23AM +0530, sonika.jindal@intel.com wrote:
> > From: Sonika Jindal <sonika.jindal@intel.com>
> > 
> > v2: Reading DP_EDP_REV, only when DISPLAY_CONTROL_CAPABLE field is set (Satheesh)
> > 
> > v3: Moving the utility function to drm_dp_helper (Daniel)
> > 
> > Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c |   15 +++++++++++++++
> >  include/drm/drm_dp_helper.h     |    2 ++
> >  2 files changed, 17 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > index 08e33b8..a54a760 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -768,3 +768,18 @@ void drm_dp_aux_unregister(struct drm_dp_aux *aux)
> >  	i2c_del_adapter(&aux->ddc);
> >  }
> >  EXPORT_SYMBOL(drm_dp_aux_unregister);
> > +
> > +bool drm_dp_is_edp_v1_4(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
> 
> I'd prefer if this didn't take a dpcd argument but rather directly
> accessed the DP_EDP_CONFIGURATION_CAP register so that it can be used
> directly rather than rely on the driver to have read a dpcd block in the
> appropriate format.

The idea is that you'd grab the DPCD field anyway since it's needed all
over the place. We have a pile of helpers already that take exactly this
block and decode parts of it. So I think this makes sense - dp aux is fast
but not entirely free, so caching seems useful.

It's a bit strange then that this helper reads more code, but I guess you
really only care about the edp_rev field if you want the edp revision, and
with your interface suggestion I don't think we'd ever need to read this
again.

So for me the input fields make sense. I agree that for the output of the
function an enum with all the edp revisions is better.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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