Re: [PATCH 1/4] drm/connector: Add data polarity flags

[Maxime Ripard <maxime@cerno.tech>]

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On Fri, Feb 14, 2020 at 05:13:59PM +0100, Sam Ravnborg wrote:
> Hi Maxime.
>
> On Fri, Feb 14, 2020 at 01:24:38PM +0100, Maxime Ripard wrote:
> > Some LVDS encoders can change the polarity of the data signals being
> > sent. Add a DRM bus flag to reflect this.
> >
> > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > ---
> >  include/drm/drm_connector.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > index 221910948b37..9a08fe6ab7c2 100644
> > --- a/include/drm/drm_connector.h
> > +++ b/include/drm/drm_connector.h
> > @@ -330,6 +330,8 @@ enum drm_panel_orientation {
> >   *					edge of the pixel clock
> >   * @DRM_BUS_FLAG_SHARP_SIGNALS:		Set if the Sharp-specific signals
> >   *					(SPL, CLS, PS, REV) must be used
> > + * @DRM_BUS_FLAG_DATA_LOW:		The Data signals are active low
> > + * @DRM_BUS_FLAG_DATA_HIGH:		The Data signals are active high
> Reading the description of these falgs always confuses me.
> In this case if neither bit 9 nor bit 10 is set then the data signals
> are netiher active low nor active high.
> So what can I then expect?
>
> We have the same logic loophole for DRM_BUS_FLAG_SYNC_SAMPLE_POSEDGE
> and DRM_BUS_FLAG_SYNC_SAMPLE_NEGEDGE.
> So it is not new, but can we do better here?

Honestly, I don't really get it either. I *think* this is to handle
the sampling / output inversion properly which wouldn't be possible if
this was only a bit set or not.

Maxime

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