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.
+ */
+ bool disable_wifi_frequencies;
+
struct cec_adapter *cec_adap;
struct cec_msg cec_rx_msg;
bool cec_tx_ok;
--
2.26.2
