2018-05-29 15:17 GMT+09:00 Hans Verkuil <hverkuil@xxxxxxxxx>:
> Hi Akinobu,
>
> On 05/27/2018 05:30 PM, Akinobu Mita wrote:
>> The open() operation for the pxa_camera driver always calls s_power()
>> operation to put its subdevice sensor in normal operation mode, and the
>> release() operation always call s_power() operation to put the subdevice
>> in power saving mode.
>>
>> This requires the subdevice sensor driver to keep track of its power
>> state in order to avoid putting the subdevice in power saving mode while
>> the device is still opened by some users.
>>
>> Many subdevice drivers handle it by the boilerplate code that increments
>> and decrements an internal counter in s_power() like below:
>>
>> /*
>> * If the power count is modified from 0 to != 0 or from != 0 to 0,
>> * update the power state.
>> */
>> if (sensor->power_count == !on) {
>> ret = ov5640_set_power(sensor, !!on);
>> if (ret)
>> goto out;
>> }
>>
>> /* Update the power count. */
>> sensor->power_count += on ? 1 : -1;
>>
>> However, some subdevice drivers don't handle it and may cause a problem
>> with the pxa_camera driver if the video device is opened by more than
>> two users at the same time.
>>
>> Instead of propagating the boilerplate code for each subdevice driver
>> that implement s_power, this introduces an trick that many V4L2 drivers
>> are using with v4l2_fh_is_singular_file().
>>
>> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
>> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
>> Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
>> ---
>> * v2
>> - Print warning message when s_power() is failed. (not printing warning
>> when _vb2_fop_release() is failed as it always returns zero for now)
>
> Please note that v1 has already been merged, so if you can make a v3 rebased
> on top of the latest media_tree master branch, then I'll queue that up for
> 4.18.
OK. There are several calls to s_power in this driver, so I'll make
a patch to add a wrapper function that prints warning message and
replace s_power calls with it.
I realized that s_power calls in suspend/resume ignore -ENOIOCTLCMD
error and other s_power calls also should ignore it. So I'll include
the check in the wrapper function.
