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

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

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@xxxxxxxxxx>
>
> ---
>
> 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...'

Assuming that the display mode still works

Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

> +	 */
> +	bool disable_wifi_frequencies;
> +
>   	struct cec_adapter *cec_adap;
>   	struct cec_msg cec_rx_msg;
>   	bool cec_tx_ok;

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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