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

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@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@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@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