[PATCH 1/2] drm/vc4: hdmi: Disable Wifi Frequencies

[Maxime Ripard]

Hi Daniel,

On Mon, Sep 28, 2020 at 11:02:11AM +0200, Daniel Vetter wrote:
> On Mon, Sep 28, 2020 at 9:06 AM Maxime Ripard <maxime at cerno.tech> wrote:
> >
> > There's cross-talk on the RPi4 between the 2.4GHz channels used by the WiFi
> > chip and some resolutions, most notably 1440p at 60Hz.
> >
> > In such a case, we can either reject entirely the mode, or lower slightly
> > the pixel frequency to remove the overlap. Let's go for the latter.
> >
> > Signed-off-by: Maxime Ripard <maxime at cerno.tech>
> > ---
> >  .../bindings/display/brcm,bcm2711-hdmi.yaml        |  6 ++++++
> >  drivers/gpu/drm/vc4/vc4_hdmi.c                     | 14 +++++++++++++-
> >  drivers/gpu/drm/vc4/vc4_hdmi.h                     |  8 ++++++++
> >  3 files changed, 27 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/display/brcm,bcm2711-hdmi.yaml b/Documentation/devicetree/bindings/display/brcm,bcm2711-hdmi.yaml
> > index 03a76729d26c..63e7fe999c0a 100644
> > --- a/Documentation/devicetree/bindings/display/brcm,bcm2711-hdmi.yaml
> > +++ b/Documentation/devicetree/bindings/display/brcm,bcm2711-hdmi.yaml
> > @@ -76,6 +76,12 @@ properties:
> >    resets:
> >      maxItems: 1
> >
> > +  raspberrypi,disable-wifi-frequencies:
> > +    type: boolean
> > +    description: >
> > +      Should the pixel frequencies in the WiFi frequencies range be
> > +      avoided?
> > +
> >  required:
> >    - compatible
> >    - reg
> > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > index acfb4e235214..74da7c00ecd0 100644
> > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > @@ -877,13 +877,22 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
> >         struct vc4_hdmi_connector_state *vc4_state = conn_state_to_vc4_hdmi_conn_state(conn_state);
> >         struct drm_display_mode *mode = &crtc_state->adjusted_mode;
> >         struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
> > -       unsigned long long pixel_rate = mode->clock * 1000;
> > +       unsigned long long pixel_rate;
> >
> >         if (vc4_hdmi->variant->broken_odd_h_timings &&
> >             ((mode->hdisplay % 2) || (mode->hsync_start % 2) ||
> >              (mode->hsync_end % 2) || (mode->htotal % 2)))
> >                 return -EINVAL;
> >
> > +       /*
> > +        * The 1440p at 60 pixel rate is in the same range than the WiFi
> > +        * channels. Slightly lower the frequency to bring it out of the
> > +        * WiFi range.
> > +        */
> > +       if (vc4_hdmi->disable_wifi_frequencies && mode->clock == 241500)
> > +               mode->clock = 238560;
> 
> Don't you want to map for a (narrow) range of frequencies here? Just
> for that infamous 60p vs 59.99p thing and similar. And I think that
> would still be in that band you want to avoid.

Testing for a range seems better indeed, I'll send a new version

Thanks!
Maxime
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