[PATCH] drm/sun4i: hdmi: Fix usage of TMDS clock

[PATCH] drm/sun4i: hdmi: Fix usage of TMDS clock

[Priit Laes]

From: Priit Laes <priit.laes@paf.com>

Although TMDS clock is required for HDMI to properly function,
nobody called clk_prepare_enable(). This fixes reference counting
issues and makes sure clock is running when it needs to be running.

Due to TDMS clock being parent clock for DDC clock, TDMS clock
was turned on/off for each EDID probe, causing spurious failures
for certain HDMI/DVI screens.

Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support")

Signed-off-by: Priit Laes <priit.laes@paf.com>
---
 drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
index 061d2e0d9011..25f4d676fd82 100644
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
@@ -92,6 +92,8 @@ static void sun4i_hdmi_disable(struct drm_encoder *encoder)
 	val = readl(hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
 	val &= ~SUN4I_HDMI_VID_CTRL_ENABLE;
 	writel(val, hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
+
+	clk_disable_unprepare(hdmi->tmds_clk);
 }
 
 static void sun4i_hdmi_enable(struct drm_encoder *encoder)
@@ -112,6 +114,8 @@ static void sun4i_hdmi_enable(struct drm_encoder *encoder)
 		val |= SUN4I_HDMI_VID_CTRL_HDMI_MODE;
 
 	writel(val, hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
+
+	clk_prepare_enable(hdmi->tmds_clk);
 }
 
 static void sun4i_hdmi_mode_set(struct drm_encoder *encoder,
-- 
2.11.0

Re: [PATCH] drm/sun4i: hdmi: Fix usage of TMDS clock

[Maxime Ripard]

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On Tue, Jan 22, 2019 at 09:32:32AM +0200, Priit Laes wrote:
> From: Priit Laes <priit.laes@paf.com>
> 
> Although TMDS clock is required for HDMI to properly function,
> nobody called clk_prepare_enable(). This fixes reference counting
> issues and makes sure clock is running when it needs to be running.
> 
> Due to TDMS clock being parent clock for DDC clock, TDMS clock
> was turned on/off for each EDID probe, causing spurious failures
> for certain HDMI/DVI screens.
> 
> Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support")
> 
> Signed-off-by: Priit Laes <priit.laes@paf.com>
> ---
>  drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> index 061d2e0d9011..25f4d676fd82 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> @@ -92,6 +92,8 @@ static void sun4i_hdmi_disable(struct drm_encoder *encoder)
>  	val = readl(hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
>  	val &= ~SUN4I_HDMI_VID_CTRL_ENABLE;
>  	writel(val, hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
> +
> +	clk_disable_unprepare(hdmi->tmds_clk);
>  }
>  
>  static void sun4i_hdmi_enable(struct drm_encoder *encoder)
> @@ -112,6 +114,8 @@ static void sun4i_hdmi_enable(struct drm_encoder *encoder)
>  		val |= SUN4I_HDMI_VID_CTRL_HDMI_MODE;
>  
>  	writel(val, hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
> +
> +	clk_prepare_enable(hdmi->tmds_clk);

We'll probably need to enable that clock to send the infoframes as
well. I moved it earlier (and that allows the enable and disable
function to be symetric as well).

Thanks for figuring this out!
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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