linux-kernel - Re: [PATCH v5 3/6] ov5670: Support probe whilst the device is in a low power state

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Date:   Wed, 12 Aug 2020 12:22:15 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Bingbu Cao <bingbu.cao@...ux.intel.com>
Cc:     linux-i2c@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-acpi@...r.kernel.org, Bingbu Cao <bingbu.cao@...el.com>,
        linux-media@...r.kernel.org,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@...el.com>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rajmohan.mani@...el.com, Tomasz Figa <tfiga@...omium.org>,
        "Qiu, Tian Shu" <tian.shu.qiu@...el.com>
Subject: Re: [PATCH v5 3/6] ov5670: Support probe whilst the device is in a
 low power state

Hi Bingbu,

Thanks for the review.

On Wed, Aug 12, 2020 at 05:12:28PM +0800, Bingbu Cao wrote:
> 
> 
> On 8/10/20 10:27 PM, Sakari Ailus wrote:
> > Tell ACPI device PM code that the driver supports the device being in a
> > low power state when the driver's probe function is entered.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > ---
> >  drivers/media/i2c/ov5670.c | 23 ++++++++++++++---------
> >  1 file changed, 14 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/ov5670.c b/drivers/media/i2c/ov5670.c
> > index f26252e35e08d..1f75b888d2a18 100644
> > --- a/drivers/media/i2c/ov5670.c
> > +++ b/drivers/media/i2c/ov5670.c
> > @@ -2456,6 +2456,7 @@ static int ov5670_probe(struct i2c_client *client)
> >  	struct ov5670 *ov5670;
> >  	const char *err_msg;
> >  	u32 input_clk = 0;
> > +	bool low_power;
> >  	int ret;
> >  
> >  	device_property_read_u32(&client->dev, "clock-frequency", &input_clk);
> > @@ -2472,11 +2473,14 @@ 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;
> > +	low_power = acpi_dev_state_low_power(&client->dev);
> > +	if (!low_power) {
> > +		/* Check module identity */
> > +		ret = ov5670_identify_module(ov5670);
> > +		if (ret) {
> > +			err_msg = "ov5670_identify_module() error";
> > +			goto error_print;
> > +	
> 
> Sakari, thanks for your patch.
> one question - With this change, there will be no chance for driver to guarantee
> that the camera sensor plugged in is the camera that the matched driver actually
> can drive until try to streaming the camera, so is it necessary to return
> appropriate error in .s_stream ops to notify user it is not the hardware that
> current driver can drive? if no other better way.

Indeed sensor identification is now skipped in probe. I'll add that for v6
--- and check other drivers, too.

-- 
Kind regards,

Sakari Ailus