Re: [PATCH v2 2/2] rcar-csi2: Use standby mode instead of resetting

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Niklas,

Thank you for the patch.

On Sat, Mar 09, 2019 at 12:47:22AM +0100, Niklas Söderlund wrote:
> Later versions of the datasheet updates the reset procedure to more
> closely resemble the standby mode. Update the driver to enter and exit
> the standby mode instead of resetting the hardware before and after
> streaming is started and stopped.

I was mislead thinking this added support for module reset in addition
to software reset (SRST_SRST-, but it actually removes the software
reset completely. Should the commit message make this clear ?

> While at it break out the full start and stop procedures from
> rcsi2_s_stream() into the existing helper functions.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> ---
>  drivers/media/platform/rcar-vin/Kconfig     |  1 +
>  drivers/media/platform/rcar-vin/rcar-csi2.c | 69 +++++++++++++--------
>  2 files changed, 43 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/media/platform/rcar-vin/Kconfig b/drivers/media/platform/rcar-vin/Kconfig
> index e3eb8fee253658da..f26f47e3bcf44825 100644
> --- a/drivers/media/platform/rcar-vin/Kconfig
> +++ b/drivers/media/platform/rcar-vin/Kconfig
> @@ -3,6 +3,7 @@ config VIDEO_RCAR_CSI2
>  	tristate "R-Car MIPI CSI-2 Receiver"
>  	depends on VIDEO_V4L2 && VIDEO_V4L2_SUBDEV_API && OF
>  	depends on ARCH_RENESAS || COMPILE_TEST
> +	select RESET_CONTROLLER
>  	select V4L2_FWNODE
>  	help
>  	  Support for Renesas R-Car MIPI CSI-2 receiver.
> diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
> index f64528d2be3c95dd..7a1c9b549e0fffc6 100644
> --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> @@ -14,6 +14,7 @@
>  #include <linux/of_graph.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/reset.h>
>  #include <linux/sys_soc.h>
>  
>  #include <media/v4l2-ctrls.h>
> @@ -350,6 +351,7 @@ struct rcar_csi2 {
>  	struct device *dev;
>  	void __iomem *base;
>  	const struct rcar_csi2_info *info;
> +	struct reset_control *rstc;
>  
>  	struct v4l2_subdev subdev;
>  	struct media_pad pads[NR_OF_RCAR_CSI2_PAD];
> @@ -387,11 +389,19 @@ static void rcsi2_write(struct rcar_csi2 *priv, unsigned int reg, u32 data)
>  	iowrite32(data, priv->base + reg);
>  }
>  
> -static void rcsi2_reset(struct rcar_csi2 *priv)
> +static void rcsi2_enter_standby(struct rcar_csi2 *priv)
>  {
> -	rcsi2_write(priv, SRST_REG, SRST_SRST);
> +	rcsi2_write(priv, PHYCNT_REG, 0);
> +	rcsi2_write(priv, PHTC_REG, PHTC_TESTCLR);
> +	reset_control_assert(priv->rstc);
>  	usleep_range(100, 150);
> -	rcsi2_write(priv, SRST_REG, 0);
> +	pm_runtime_put(priv->dev);
> +}
> +
> +static void rcsi2_exit_standby(struct rcar_csi2 *priv)
> +{
> +	pm_runtime_get_sync(priv->dev);
> +	reset_control_deassert(priv->rstc);
>  }
>  
>  static int rcsi2_wait_phy_start(struct rcar_csi2 *priv)
> @@ -462,7 +472,7 @@ static int rcsi2_calc_mbps(struct rcar_csi2 *priv, unsigned int bpp)
>  	return mbps;
>  }
>  
> -static int rcsi2_start(struct rcar_csi2 *priv)
> +static int rcsi2_start_receiver(struct rcar_csi2 *priv)
>  {
>  	const struct rcar_csi2_format *format;
>  	u32 phycnt, vcdt = 0, vcdt2 = 0;
> @@ -506,7 +516,6 @@ static int rcsi2_start(struct rcar_csi2 *priv)
>  
>  	/* Init */
>  	rcsi2_write(priv, TREF_REG, TREF_TREF);
> -	rcsi2_reset(priv);
>  	rcsi2_write(priv, PHTC_REG, 0);
>  
>  	/* Configure */
> @@ -564,19 +573,36 @@ static int rcsi2_start(struct rcar_csi2 *priv)
>  	return 0;
>  }
>  
> +static int rcsi2_start(struct rcar_csi2 *priv)
> +{
> +	int ret;
> +
> +	rcsi2_exit_standby(priv);
> +
> +	ret = rcsi2_start_receiver(priv);

The rcsi2_start_receiver() function should be split in two, with
rcsi2_wait_phy_start() and below being performed after starting the
source. Alternatively you could start the source first, but I think a
split would be better.

> +	if (ret) {
> +		rcsi2_enter_standby(priv);
> +		return ret;
> +	}
> +
> +	ret = v4l2_subdev_call(priv->remote, video, s_stream, 1);
> +	if (ret) {
> +		rcsi2_enter_standby(priv);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  static void rcsi2_stop(struct rcar_csi2 *priv)
>  {
> -	rcsi2_write(priv, PHYCNT_REG, 0);
> -
> -	rcsi2_reset(priv);
> -
> -	rcsi2_write(priv, PHTC_REG, PHTC_TESTCLR);
> +	v4l2_subdev_call(priv->remote, video, s_stream, 0);
> +	rcsi2_enter_standby(priv);

Shouldn't you enter standby before stopping the source ? Otherwise
there's a risk of CSI errors being detected. Figures 25.23.1 and 25.23.2
seem to agree with me.

>  }
>  
>  static int rcsi2_s_stream(struct v4l2_subdev *sd, int enable)
>  {
>  	struct rcar_csi2 *priv = sd_to_csi2(sd);
> -	struct v4l2_subdev *nextsd;
>  	int ret = 0;
>  
>  	mutex_lock(&priv->lock);
> @@ -586,27 +612,12 @@ static int rcsi2_s_stream(struct v4l2_subdev *sd, int enable)
>  		goto out;
>  	}
>  
> -	nextsd = priv->remote;
> -
>  	if (enable && priv->stream_count == 0) {
> -		pm_runtime_get_sync(priv->dev);
> -
>  		ret = rcsi2_start(priv);
> -		if (ret) {
> -			pm_runtime_put(priv->dev);
> +		if (ret)
>  			goto out;
> -		}
> -
> -		ret = v4l2_subdev_call(nextsd, video, s_stream, 1);
> -		if (ret) {
> -			rcsi2_stop(priv);
> -			pm_runtime_put(priv->dev);
> -			goto out;
> -		}
>  	} else if (!enable && priv->stream_count == 1) {
>  		rcsi2_stop(priv);
> -		v4l2_subdev_call(nextsd, video, s_stream, 0);
> -		pm_runtime_put(priv->dev);
>  	}
>  
>  	priv->stream_count += enable ? 1 : -1;
> @@ -936,6 +947,10 @@ static int rcsi2_probe_resources(struct rcar_csi2 *priv,
>  	if (irq < 0)
>  		return irq;
>  
> +	priv->rstc = devm_reset_control_get(&pdev->dev, NULL);
> +	if (IS_ERR(priv->rstc))
> +		return PTR_ERR(priv->rstc);
> +
>  	return 0;
>  }
>  

-- 
Regards,

Laurent Pinchart