Re: [PATCH 3/5] ov5670: Support probe whilst the device is off

[Tomasz Figa <tfiga@chromium.org>]

Hi Sakari,

On Fri, May 10, 2019 at 01:09:28PM +0300, Sakari Ailus wrote:
> Tell ACPI device PM code that the driver supports the device being powered
> off when the driver's probe function is entered.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/i2c/ov5670.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov5670.c b/drivers/media/i2c/ov5670.c
> index 041fcbb4eebdf..57e8b92f90e09 100644
> --- a/drivers/media/i2c/ov5670.c
> +++ b/drivers/media/i2c/ov5670.c
> @@ -2444,6 +2444,7 @@ static int ov5670_probe(struct i2c_client *client)
>  	struct ov5670 *ov5670;
>  	const char *err_msg;
>  	u32 input_clk = 0;
> +	bool powered_off;
>  	int ret;
>  
>  	device_property_read_u32(&client->dev, "clock-frequency", &input_clk);
> @@ -2460,11 +2461,14 @@ static int ov5670_probe(struct i2c_client *client)
>  	/* Initialize subdev */
>  	v4l2_i2c_subdev_init(&ov5670->sd, client, &ov5670_subdev_ops);
>  
> -	/* Check module identity */
> -	ret = ov5670_identify_module(ov5670);
> -	if (ret) {
> -		err_msg = "ov5670_identify_module() error";
> -		goto error_print;
> +	powered_off = acpi_dev_powered_off_for_probe(&client->dev);
> +	if (!powered_off) {
> +		/* Check module identity */
> +		ret = ov5670_identify_module(ov5670);
> +		if (ret) {
> +			err_msg = "ov5670_identify_module() error";
> +			goto error_print;
> +		}
>  	}

I don't like the fact that we can't detect any hardware connection issue
here anymore and we would actually get some obscure failure when we
actually start streaming.

Wouldn't it be possible to still keep this behavior of not powering on
the device at boot-up if no driver is bound and then have this driver
built as a module and loaded later when the camera is to be used for the
first time after the system boots?

Best regards,
Tomasz