Re: [PATCH v2 2/3] drm/vc4: hdmi: Disable Wifi Frequencies

[Maxime Ripard <maxime@cerno.tech>]

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On Thu, Nov 19, 2020 at 10:20:25AM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 29.10.20 um 14:40 schrieb Maxime Ripard:
> > 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>
> > 
> > ---
> > 
> > Changes from v1:
> >    - Change the name of the property
> >    - Test for a range instead of an exact frequency
> > ---
> >   drivers/gpu/drm/vc4/vc4_hdmi.c | 21 +++++++++++++++++++++
> >   drivers/gpu/drm/vc4/vc4_hdmi.h |  8 ++++++++
> >   2 files changed, 29 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > index 506c12454086..0d72e519aec4 100644
> > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > @@ -760,6 +760,9 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
> >   {
> >   }
> > +#define WIFI_2_4GHz_CH1_MIN_FREQ	2400000000ULL
> > +#define WIFI_2_4GHz_CH1_MAX_FREQ	2422000000ULL
> > +
> >   static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
> >   					 struct drm_crtc_state *crtc_state,
> >   					 struct drm_connector_state *conn_state)
> > @@ -767,12 +770,27 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
> >   	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 tmds_rate;
> >   	if (vc4_hdmi->variant->unsupported_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 first
> > +	 * WiFi channel (between 2.4GHz and 2.422GHz with 22MHz
> > +	 * bandwidth). Slightly lower the frequency to bring it out of
> > +	 * the WiFi range.
> > +	 */
> > +	tmds_rate = pixel_rate * 10;
> > +	if (vc4_hdmi->disable_wifi_frequencies &&
> > +	    (tmds_rate >= WIFI_2_4GHz_CH1_MIN_FREQ &&
> > +	     tmds_rate <= WIFI_2_4GHz_CH1_MAX_FREQ)) {
> > +		mode->clock = 238560;
> > +		pixel_rate = mode->clock * 1000;
> > +	}
> > +
> >   	if (pixel_rate > vc4_hdmi->variant->max_pixel_clock)
> >   		return -EINVAL;
> > @@ -1717,6 +1735,9 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
> >   		vc4_hdmi->hpd_active_low = hpd_gpio_flags & OF_GPIO_ACTIVE_LOW;
> >   	}
> > +	vc4_hdmi->disable_wifi_frequencies =
> > +		of_property_read_bool(dev->of_node, "wifi-2.4ghz-coexistence");
> > +
> >   	pm_runtime_enable(dev);
> >   	drm_simple_encoder_init(drm, encoder, DRM_MODE_ENCODER_TMDS);
> > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> > index 6815e93b1a48..3843be830601 100644
> > --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> > @@ -142,6 +142,14 @@ struct vc4_hdmi {
> >   	int hpd_gpio;
> >   	bool hpd_active_low;
> > +	/*
> > +	 * On some systems (like the RPi4), some modes are in the same
> > +	 * frequency range than the WiFi channels (1440p@60Hz for
> > +	 * example). Should we take evasive actions because that system
> > +	 * has a wifi adapter.
> 
> The final sentence sounds like a question. Maybe just write 'Take evasive
> actions if...'

This was definitely a question, I've added the question mark and applied
the two first patches

> Assuming that the display mode still works
> 
> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

Thanks!
Maxime

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