Re: [PATCH 2/4] drm/vc4: prepare for CEC support

From: Eric Anholt <eric@anholt.net>
To: Hans Verkuil <hverkuil@xs4all.nl>, linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org,
	Hans Verkuil <hans.verkuil@cisco.com>,
	boris.brezillon@free-electrons.com
Subject: Re: [PATCH 2/4] drm/vc4: prepare for CEC support
Date: Wed, 12 Jul 2017 11:42:53 -0700	[thread overview]
Message-ID: <87fue1h4ya.fsf@eliezer.anholt.net> (raw)
In-Reply-To: <20170711112021.38525-3-hverkuil@xs4all.nl>

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Hans Verkuil <hverkuil@xs4all.nl> writes:

> From: Hans Verkuil <hans.verkuil@cisco.com>
>
> In order to support CEC the hsm clock needs to be enabled in
> vc4_hdmi_bind(), not in vc4_hdmi_encoder_enable(). Otherwise you wouldn't
> be able to support CEC when there is no hotplug detect signal, which is
> required by some monitors that turn off the HPD when in standby, but keep
> the CEC bus alive so they can be woken up.
>
> The HDMI core also has to be enabled in vc4_hdmi_bind() for the same
> reason.
>
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

Ccing Boris, I'd love to see what he thinks of this and if we can do any
better.

Hans, is it true that CEC needs to be on always, or could it only be
enabled when somebody is listening to messages?

>  drivers/gpu/drm/vc4/vc4_hdmi.c | 59 +++++++++++++++++++++---------------------
>  1 file changed, 29 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index ed63d4e85762..e0104f96011e 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -463,11 +463,6 @@ static void vc4_hdmi_encoder_disable(struct drm_encoder *encoder)
>  	HD_WRITE(VC4_HD_VID_CTL,
>  		 HD_READ(VC4_HD_VID_CTL) & ~VC4_HD_VID_CTL_ENABLE);
>  
> -	HD_WRITE(VC4_HD_M_CTL, VC4_HD_M_SW_RST);
> -	udelay(1);
> -	HD_WRITE(VC4_HD_M_CTL, 0);
> -
> -	clk_disable_unprepare(hdmi->hsm_clock);
>  	clk_disable_unprepare(hdmi->pixel_clock);
>  
>  	ret = pm_runtime_put(&hdmi->pdev->dev);
> @@ -509,16 +504,6 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
>  		return;
>  	}
>  
> -	/* This is the rate that is set by the firmware.  The number
> -	 * needs to be a bit higher than the pixel clock rate
> -	 * (generally 148.5Mhz).
> -	 */
> -	ret = clk_set_rate(hdmi->hsm_clock, 163682864);
> -	if (ret) {
> -		DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
> -		return;
> -	}
> -
>  	ret = clk_set_rate(hdmi->pixel_clock,
>  			   mode->clock * 1000 *
>  			   ((mode->flags & DRM_MODE_FLAG_DBLCLK) ? 2 : 1));
> @@ -533,20 +518,6 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
>  		return;
>  	}
>  
> -	ret = clk_prepare_enable(hdmi->hsm_clock);
> -	if (ret) {
> -		DRM_ERROR("Failed to turn on HDMI state machine clock: %d\n",
> -			  ret);
> -		clk_disable_unprepare(hdmi->pixel_clock);
> -		return;
> -	}
> -
> -	HD_WRITE(VC4_HD_M_CTL, VC4_HD_M_SW_RST);
> -	udelay(1);
> -	HD_WRITE(VC4_HD_M_CTL, 0);
> -
> -	HD_WRITE(VC4_HD_M_CTL, VC4_HD_M_ENABLE);
> -
>  	HDMI_WRITE(VC4_HDMI_SW_RESET_CONTROL,
>  		   VC4_HDMI_SW_RESET_HDMI |
>  		   VC4_HDMI_SW_RESET_FORMAT_DETECT);
> @@ -1205,6 +1176,23 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>  		return -EPROBE_DEFER;
>  	}
>  
> +	/* This is the rate that is set by the firmware.  The number
> +	 * needs to be a bit higher than the pixel clock rate
> +	 * (generally 148.5Mhz).
> +	 */
> +	ret = clk_set_rate(hdmi->hsm_clock, 163682864);
> +	if (ret) {
> +		DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
> +		goto err_put_i2c;
> +	}
> +
> +	ret = clk_prepare_enable(hdmi->hsm_clock);
> +	if (ret) {
> +		DRM_ERROR("Failed to turn on HDMI state machine clock: %d\n",
> +			  ret);
> +		goto err_put_i2c;
> +	}
> +
>  	/* Only use the GPIO HPD pin if present in the DT, otherwise
>  	 * we'll use the HDMI core's register.
>  	 */
> @@ -1216,7 +1204,7 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>  							 &hpd_gpio_flags);
>  		if (hdmi->hpd_gpio < 0) {
>  			ret = hdmi->hpd_gpio;
> -			goto err_put_i2c;
> +			goto err_unprepare_hsm;
>  		}
>  
>  		hdmi->hpd_active_low = hpd_gpio_flags & OF_GPIO_ACTIVE_LOW;
> @@ -1224,6 +1212,14 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>  
>  	vc4->hdmi = hdmi;
>  
> +	/* HDMI core must be enabled. */
> +	if (!(HD_READ(VC4_HD_M_CTL) & VC4_HD_M_ENABLE)) {
> +		HD_WRITE(VC4_HD_M_CTL, VC4_HD_M_SW_RST);
> +		udelay(1);
> +		HD_WRITE(VC4_HD_M_CTL, 0);
> +
> +		HD_WRITE(VC4_HD_M_CTL, VC4_HD_M_ENABLE);
> +	}

I'm wondering if there's any impact from leaving VC4_HD_M_ENABLE on
while the HDMI power domain is off.  I don't quite understand the role
of the power domain, and I've fired off an email internally to check if
there are any experts on this hardware still around.

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