On 02/21/2018 01:02 AM, Laurent Pinchart wrote:
> Hi Hans,
>
> Thank you for the patch.
>
> On Tuesday, 20 February 2018 11:44:20 EET Hans Verkuil wrote:
>> The v4l2_subdev core s_power op was used for two different things: power
>> on/off sensors or video decoders/encoders and to put a tuner in standby
>> (and only the tuner!). There is no 'tuner wakeup' op, that's done
>> automatically when the tuner is accessed.
>>
>> The danger with calling (s_power, 0) to put a tuner into standby is that it
>> is usually broadcast for all subdevs. So a video receiver subdev that
>> supports s_power will also be powered off, and since there is no
>> corresponding (s_power, 1) they will never be powered on again.
>>
>> In addition, this is specifically meant for tuners only since they draw the
>> most current.
>>
>> This patch adds a new tuner op called 'standby' and replaces all calls to
>> (core, s_power, 0) by (tuner, standby). This prevents confusion between the
>> two uses of s_power. Note that there is no overlap: bridge drivers either
>> just want to put the tuner into standby, or they deal with powering on/off
>> sensors. Never both.
>>
>> This also makes it easier to replace s_power for the remaining bridge
>> drivers with some PM code later.
>>
>> Whether we want something cleaner for tuners in the future is a separate
>> topic. There is a lot of legacy code surrounding tuners, and I am very
>> hesitant about making changes there.
>>
>> Signed-off-by: Hans Verkuil <[email protected]>
>> ---
>> Changes since v1:
>> - move the standby op to the tuner_ops, which makes much more sense.
>> ---
>
> [snip]
>
>> diff --git a/drivers/media/v4l2-core/tuner-core.c
>> b/drivers/media/v4l2-core/tuner-core.c index 82852f23a3b6..cb126baf8771
>> 100644
>> --- a/drivers/media/v4l2-core/tuner-core.c
>> +++ b/drivers/media/v4l2-core/tuner-core.c
>> @@ -1099,23 +1099,15 @@ static int tuner_s_radio(struct v4l2_subdev *sd)
>> */
>>
>> /**
>> - * tuner_s_power - controls the power state of the tuner
>> + * tuner_standby - controls the power state of the tuner
>
> I'd update the description too.
>
>> * @sd: pointer to struct v4l2_subdev
>> * @on: a zero value puts the tuner to sleep, non-zero wakes it up
>
> And this parameter doesn't exist anymore. You could have caught that by
> compiling the documentation.
Oops! I'll make a v3. Thanks for catching this.
>
>> */
>> -static int tuner_s_power(struct v4l2_subdev *sd, int on)
>> +static int tuner_standby(struct v4l2_subdev *sd)
>> {
>> struct tuner *t = to_tuner(sd);
>> struct analog_demod_ops *analog_ops = &t->fe.ops.analog_ops;
>>
>> - if (on) {
>> - if (t->standby && set_mode(t, t->mode) == 0) {
>> - dprintk("Waking up tuner\n");
>> - set_freq(t, 0);
>> - }
>> - return 0;
>> - }
>> -
>
> Interesting how this code was not used. I've had a look at tuner-core driver
> out of curiosity, it clearly shows its age :/ I2C address probing belongs to
> another century.
Not really. It's still needed for USB/PCI devices.
I was also surprised that it wasn't used. I expected to see some internal calls
to tuner_s_power(sd, 1) to turn things on, but that's not what happened.
Regards,
Hans
>
>> dprintk("Putting tuner to sleep\n");
>> t->standby = true;
>> if (analog_ops->standby)
>> @@ -1328,10 +1320,10 @@ static int tuner_command(struct i2c_client *client,
>> unsigned cmd, void *arg)
>>
>> static const struct v4l2_subdev_core_ops tuner_core_ops = {
>> .log_status = tuner_log_status,
>> - .s_power = tuner_s_power,
>> };
>>
>> static const struct v4l2_subdev_tuner_ops tuner_tuner_ops = {
>> + .standby = tuner_standby,
>> .s_radio = tuner_s_radio,
>> .g_tuner = tuner_g_tuner,
>> .s_tuner = tuner_s_tuner,
>> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
>> index 980a86c08fce..62429cd89620 100644
>> --- a/include/media/v4l2-subdev.h
>> +++ b/include/media/v4l2-subdev.h
>> @@ -224,6 +224,9 @@ struct v4l2_subdev_core_ops {
>> * struct v4l2_subdev_tuner_ops - Callbacks used when v4l device was opened
>> * in radio mode.
>> *
>> + * @standby: puts the tuner in standby mode. It will be woken up
>> + * automatically the next time it is used.
>> + *
>
> I wouldn't have dared making such a statement as I don't trust myself as
> being
> able to give such a guarantee after reading the code :-)
>
>> * @s_radio: callback that switches the tuner to radio mode.
>> * drivers should explicitly call it when a tuner ops should
>> * operate on radio mode, before being able to handle it.
>> @@ -268,6 +271,7 @@ struct v4l2_subdev_core_ops {
>> * }
>> */
>> struct v4l2_subdev_tuner_ops {
>> + int (*standby)(struct v4l2_subdev *sd);
>> int (*s_radio)(struct v4l2_subdev *sd);
>> int (*s_frequency)(struct v4l2_subdev *sd, const struct v4l2_frequency
>> *freq);
>> int (*g_frequency)(struct v4l2_subdev *sd, struct v4l2_frequency *freq);
>
