drm/vc4: hdmi: Update the CEC clock divider on HSM rate change

As part of the enable sequence we might change the HSM clock rate if the
pixel rate is different than the one we were already dealing with.

On the BCM2835 however, the CEC clock derives from the HSM clock so any
rate change will need to be reflected in the CEC clock divider to output
40kHz.

Fixes: cd4cb49d ("drm/vc4: hdmi: Adjust HSM clock rate depending on pixel rate")
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Tested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Link: https://patchwork.freedesktop.org/patch/msgid/20210111142309.193441-8-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -132,6 +132,27 @@ static void vc5_hdmi_reset(struct vc4_hdmi *vc4_hdmi)
 		   HDMI_READ(HDMI_CLOCK_STOP) | VC4_DVP_HT_CLOCK_STOP_PIXEL);
 }
 
+#ifdef CONFIG_DRM_VC4_HDMI_CEC
+static void vc4_hdmi_cec_update_clk_div(struct vc4_hdmi *vc4_hdmi)
+{
+	u16 clk_cnt;
+	u32 value;
+
+	value = HDMI_READ(HDMI_CEC_CNTRL_1);
+	value &= ~VC4_HDMI_CEC_DIV_CLK_CNT_MASK;
+
+	/*
+	 * Set the clock divider: the hsm_clock rate and this divider
+	 * setting will give a 40 kHz CEC clock.
+	 */
+	clk_cnt = clk_get_rate(vc4_hdmi->hsm_clock) / CEC_CLOCK_FREQ;
+	value |= clk_cnt << VC4_HDMI_CEC_DIV_CLK_CNT_SHIFT;
+	HDMI_WRITE(HDMI_CEC_CNTRL_1, value);
+}
+#else
+static void vc4_hdmi_cec_update_clk_div(struct vc4_hdmi *vc4_hdmi) {}
+#endif
+
 static enum drm_connector_status
 vc4_hdmi_connector_detect(struct drm_connector *connector, bool force)
 {
@@ -770,6 +791,8 @@ static void vc4_hdmi_encoder_pre_crtc_configure(struct drm_encoder *encoder,
 		return;
 	}
 
+	vc4_hdmi_cec_update_clk_div(vc4_hdmi);
+
 	/*
 	 * FIXME: When the pixel freq is 594MHz (4k60), this needs to be setup
 	 * at 300MHz.
@@ -1598,7 +1621,6 @@ static int vc4_hdmi_cec_init(struct vc4_hdmi *vc4_hdmi)
 {
 	struct cec_connector_info conn_info;
 	struct platform_device *pdev = vc4_hdmi->pdev;
-	u16 clk_cnt;
 	u32 value;
 	int ret;
 
@@ -1617,17 +1639,14 @@ static int vc4_hdmi_cec_init(struct vc4_hdmi *vc4_hdmi)
 	cec_s_conn_info(vc4_hdmi->cec_adap, &conn_info);
 
 	HDMI_WRITE(HDMI_CEC_CPU_MASK_SET, 0xffffffff);
+
 	value = HDMI_READ(HDMI_CEC_CNTRL_1);
-	value &= ~VC4_HDMI_CEC_DIV_CLK_CNT_MASK;
-	/*
-	 * Set the logical address to Unregistered and set the clock
-	 * divider: the hsm_clock rate and this divider setting will
-	 * give a 40 kHz CEC clock.
-	 */
-	clk_cnt = clk_get_rate(vc4_hdmi->hsm_clock) / CEC_CLOCK_FREQ;
-	value |= VC4_HDMI_CEC_ADDR_MASK |
-		 (clk_cnt << VC4_HDMI_CEC_DIV_CLK_CNT_SHIFT);
+	/* Set the logical address to Unregistered */
+	value |= VC4_HDMI_CEC_ADDR_MASK;
 	HDMI_WRITE(HDMI_CEC_CNTRL_1, value);
+
+	vc4_hdmi_cec_update_clk_div(vc4_hdmi);
+
 	ret = devm_request_threaded_irq(&pdev->dev, platform_get_irq(pdev, 0),
 					vc4_cec_irq_handler,
 					vc4_cec_irq_handler_thread, 0,