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

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Date:   Fri, 14 Aug 2020 12:49:44 +0800
From:   Bingbu Cao <bingbu.cao@...ux.intel.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-i2c@...r.kernel.org
Cc:     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



On 8/12/20 5:12 PM, 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.

Sakari, please ignore my previous comment, it is not related to this change. I
see the sub device open is caused by v4l_id program from udev.

> 

-- 
Best regards,
Bingbu Cao