Re: [PATCH/RFC 1/2] V4L2: soc-camera: work around unbalanced calls to .s_power()

["Frank Schäfer" <fschaefer.oss@googlemail.com>]

Hi Guennadi,

thanks for the patches and sorry for the delay.
I've tested them a few minutes ago and they are working fine.

2 minor things/questions:

1.) Why not always balance v4l2_clk_enable/disable() calls ?

2.) For someone who reads the code it likely looks a bit odd that if the
flag "unbalanced_power" is set, soc_camera balances
v4l2_clk_enable/disable but not power on/off calls (ssdd->power() calls).
So maybe "balance_clk" or "clk_balancing_needed" would be a better name
for the flag ?


Ok, let's summarize what we need:
- the 3 fake clock patches patches
- em28xx patch "make sure that all subdevices are powered on when needed"
- these 2 patches

All patches need to marked for stable (3.11).
Can you pick up my me28xx patch and send Mauro a pull request ?

Regards,
Frank

Am 21.10.2013 11:28, schrieb Guennadi Liakhovetski:
> Some non soc-camera drivers, e.g. em28xx, use subdevice drivers, originally
> written for soc-camera, which use soc_camera_power_on() and
> soc_camera_power_off() helpers to implement their .s_power() methods. Those
> helpers in turn can enable and disable a clock, if it is supplied to them
> as a parameter. This works well when camera host drivers balance their
> calls to subdevices' .s_power() methods. However, some such drivers fail to
> do that, which leads to unbalanced calls to v4l2_clk_enable() /
> v4l2_clk_disable(), which then in turn produce kernel warnings. Such
> behaviour is wrong and should be fixed, however, sometimes it is difficult,
> because some of those drivers are rather old and use lots of subdevices,
> which all should be tested after such a fix. To support such drivers this
> patch adds a work-around, allowing host drivers or platforms to set a flag,
> in which case soc-camera helpers will only enable the clock, if it is
> disabled, and disable it only once on the first call to .s_power(0).
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
>
> As promised yesterday, this is an alternative approach to fixing the 
> em28xx problem, compile tested only.
>
>  drivers/media/platform/soc_camera/soc_camera.c |   22 ++++++++++++++++------
>  include/media/soc_camera.h                     |   14 ++++++++++++++
>  2 files changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/platform/soc_camera/soc_camera.c b/drivers/media/platform/soc_camera/soc_camera.c
> index 387a232..21136a2 100644
> --- a/drivers/media/platform/soc_camera/soc_camera.c
> +++ b/drivers/media/platform/soc_camera/soc_camera.c
> @@ -71,11 +71,21 @@ static int video_dev_create(struct soc_camera_device *icd);
>  int soc_camera_power_on(struct device *dev, struct soc_camera_subdev_desc *ssdd,
>  			struct v4l2_clk *clk)
>  {
> -	int ret = clk ? v4l2_clk_enable(clk) : 0;
> -	if (ret < 0) {
> -		dev_err(dev, "Cannot enable clock: %d\n", ret);
> -		return ret;
> +	int ret;
> +	bool clock_toggle;
> +
> +	if (clk && (!ssdd->unbalanced_power ||
> +		    !test_and_set_bit(0, &ssdd->clock_state))) {
> +		ret = v4l2_clk_enable(clk);
> +		if (ret < 0) {
> +			dev_err(dev, "Cannot enable clock: %d\n", ret);
> +			return ret;
> +		}
> +		clock_toggle = true;
> +	} else {
> +		clock_toggle = false;
>  	}
> +
>  	ret = regulator_bulk_enable(ssdd->num_regulators,
>  					ssdd->regulators);
>  	if (ret < 0) {
> @@ -98,7 +108,7 @@ epwron:
>  	regulator_bulk_disable(ssdd->num_regulators,
>  			       ssdd->regulators);
>  eregenable:
> -	if (clk)
> +	if (clock_toggle)
>  		v4l2_clk_disable(clk);
>  
>  	return ret;
> @@ -127,7 +137,7 @@ int soc_camera_power_off(struct device *dev, struct soc_camera_subdev_desc *ssdd
>  		ret = ret ? : err;
>  	}
>  
> -	if (clk)
> +	if (clk && (!ssdd->unbalanced_power || test_and_clear_bit(0, &ssdd->clock_state)))
>  		v4l2_clk_disable(clk);
>  
>  	return ret;
> diff --git a/include/media/soc_camera.h b/include/media/soc_camera.h
> index 34d2414..5678a39 100644
> --- a/include/media/soc_camera.h
> +++ b/include/media/soc_camera.h
> @@ -150,6 +150,15 @@ struct soc_camera_subdev_desc {
>  	struct regulator_bulk_data *regulators;
>  	int num_regulators;
>  
> +	/*
> +	 * Set unbalanced_power to true to deal with legacy drivers, failing to
> +	 * balance their calls to subdevice's .s_power() method. clock_state is
> +	 * then used internally by helper functions, it shouldn't be touched by
> +	 * drivers or the platform code.
> +	 */
> +	bool unbalanced_power;
> +	unsigned long clock_state;
> +
>  	/* Optional callbacks to power on or off and reset the sensor */
>  	int (*power)(struct device *, int);
>  	int (*reset)(struct device *);
> @@ -206,6 +215,11 @@ struct soc_camera_link {
>  	struct regulator_bulk_data *regulators;
>  	int num_regulators;
>  
> +	/* Set by platforms to handle misbehaving drivers */
> +	bool unbalanced_power;
> +	/* Used by soc-camera helper functions */
> +	unsigned long clock_state;
> +
>  	/* Optional callbacks to power on or off and reset the sensor */
>  	int (*power)(struct device *, int);
>  	int (*reset)(struct device *);