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

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Message-ID: <20190122091727.fksox7poqxvt5umu@flea>
Date:   Tue, 22 Jan 2019 10:17:27 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Priit Laes <plaes@...es.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Chen-Yu Tsai <wens@...e.org>, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Priit Laes <priit.laes@....com>
Subject: Re: [PATCH] drm/sun4i: hdmi: Fix usage of TMDS clock

On Tue, Jan 22, 2019 at 09:32:32AM +0200, Priit Laes wrote:
> From: Priit Laes <priit.laes@....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@....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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