Re: [PATCH] dw9714: Initial driver for dw9714 VCM

[Tomasz Figa <tfiga@chromium.org>]

On Tue, May 9, 2017 at 6:40 PM, Sakari Ailus <sakari.ailus@iki.fi> wrote:
> Hi Tomasz,
>
> On Tue, May 09, 2017 at 04:30:40PM +0800, Tomasz Figa wrote:
>> Hi Sakari,
>>
>> On Tue, May 9, 2017 at 4:55 AM, Sakari Ailus <sakari.ailus@iki.fi> wrote:
>> > Hi Rajmohan,
>> >
>> > A few comments below...
>> >
>> > On Sun, May 07, 2017 at 04:33:24AM -0700, rajmohan.mani@intel.com wrote:
>> [snip]
>> >> +     rval = v4l2_async_register_subdev(&dw9714_dev->sd);
>> >> +     if (rval < 0)
>> >> +             goto err_cleanup;
>> >> +
>> >> +     pm_runtime_enable(&client->dev);
>> >
>> > Getting PM runtime right doesn't seem to be easy. :-I
>> >
>> > pm_runtime_enable() alone doesn't do the trick. I wonder if adding
>> > pm_runtime_suspend() would do the trick.
>>
>> Is this something specific for I2C devices? For platform devices,
>> typically pm_runtime_enable() is the only thing you would need to do.
>
> I think you're right --- driver_probe_device() will call pm_request_idle()
> to the device right after probe. So indeed calling pm_runtime_enable() is
> enough.
>
>> >> +
>> >> +     return 0;
>> >> +
>> >> +err_cleanup:
>> >> +     dw9714_subdev_cleanup(dw9714_dev);
>> >> +     dev_err(&client->dev, "Probe failed: %d\n", rval);
>> >> +     return rval;
>> >> +}
>> >> +
>> >> +static int dw9714_remove(struct i2c_client *client)
>> >> +{
>> >> +     struct v4l2_subdev *sd = i2c_get_clientdata(client);
>> >> +     struct dw9714_device *dw9714_dev = container_of(sd,
>> >> +                                                     struct dw9714_device,
>> >> +                                                     sd);
>> >> +
>> >> +     pm_runtime_disable(&client->dev);
>> >> +     dw9714_subdev_cleanup(dw9714_dev);
>> >> +
>> >> +     return 0;
>> >> +}
>> >> +
>> >> +#ifdef CONFIG_PM
>> >> +
>> >> +static int dw9714_runtime_suspend(struct device *dev)
>> >> +{
>> >> +     return 0;
>> >> +}
>> >> +
>> >> +static int dw9714_runtime_resume(struct device *dev)
>> >> +{
>> >> +     return 0;
>> >
>> > I think it'd be fine to remove empty callbacks.
>>
>> It's actually a bit more complicated (if a PM domain is attached, the
>> callbacks must be present), however in case of external I2C devices it
>> should be fine indeed. However, AFAIK, pm_runtime_no_callbacks()
>> should be called.
>
> I wonder if I'm missing something --- acpi_subsys_runtime_resume() first
> calls acpi_dev_runtime_resume() and if all goes well, the proceeds to call
> pm_generic_runtime_resume() which calls device's runtime_resume() if it's
> non-NULL.
>
> In other words, having a runtime_resume() and runtime_suspend() callbacks
> that return zero is equivalent of having neither of the callbacks.

Ah, I missed the fact this device is instantiated by ACPI and it has
different handling of runtime PM, which apparently means it doesn't
use the code paths affected by the PM domain thing I mentioned.

>
>>
>> >
>> >> +}
>> >> +
>> >> +/* This function sets the vcm position, so it consumes least current */
>> >> +static int dw9714_suspend(struct device *dev)
>> >> +{
>> >> +     struct i2c_client *client = to_i2c_client(dev);
>> >> +     struct v4l2_subdev *sd = i2c_get_clientdata(client);
>> >> +     struct dw9714_device *dw9714_dev = container_of(sd,
>> >> +                                                     struct dw9714_device,
>> >> +                                                     sd);
>> >> +     int ret, val;
>> >> +
>> >> +     dev_dbg(dev, "%s\n", __func__);
>> >> +
>> >> +     for (val = dw9714_dev->current_val & ~(DW9714_CTRL_STEPS - 1);
>> >> +          val >= 0; val -= DW9714_CTRL_STEPS) {
>> >> +             ret = dw9714_i2c_write(client,
>> >> +                                    DW9714_VAL((u16) val, DW9714_DEFAULT_S));
>> >> +             if (ret)
>> >> +                     dev_err(dev, "%s I2C failure: %d", __func__, ret);
>> >> +             usleep_range(DW9714_CTRL_DELAY_US, DW9714_CTRL_DELAY_US + 10);
>> >> +     }
>> >> +     return 0;
>> >> +}
>> >> +
>> >> +/*
>> >> + * This function sets the vcm position, so the focus position is set
>> >> + * closer to the camera
>> >> + */
>> >> +static int dw9714_resume(struct device *dev)
>> >> +{
>> >> +     struct i2c_client *client = to_i2c_client(dev);
>> >> +     struct v4l2_subdev *sd = i2c_get_clientdata(client);
>> >> +     struct dw9714_device *dw9714_dev = container_of(sd,
>> >> +                                                     struct dw9714_device,
>> >> +                                                     sd);
>> >> +     int ret, val;
>> >> +
>> >> +     dev_dbg(dev, "%s\n", __func__);
>> >> +
>> >> +     for (val = dw9714_dev->current_val % DW9714_CTRL_STEPS;
>> >> +          val < dw9714_dev->current_val + DW9714_CTRL_STEPS - 1;
>> >> +          val += DW9714_CTRL_STEPS) {
>> >> +             ret = dw9714_i2c_write(client,
>> >> +                                    DW9714_VAL((u16) val, DW9714_DEFAULT_S));
>> >> +             if (ret)
>> >> +                     dev_err(dev, "%s I2C failure: %d", __func__, ret);
>> >> +             usleep_range(DW9714_CTRL_DELAY_US, DW9714_CTRL_DELAY_US + 10);
>> >> +     }
>> >> +
>> >> +     /* restore v4l2 control values */
>> >> +     ret = v4l2_ctrl_handler_setup(&dw9714_dev->ctrls_vcm);
>> >
>> > Doesn't this need to be done for runtime_resume as well?
>>
>> This driver doesn't seem to be doing any physical power off in its
>> runtime_suspend and I don't expect an I2C device to be put in a PM
>> domain, so possibly no need for it.
>
> I'd expect runtime PM suspend callback to power the device off through ACPI
> PM. For this reason the device state must be restored when it's powered on,
> i.e. its runtime_resume callback.

Ah, again ACPI here, that's something not usual for me. Sorry for the noise.

Best regards,
Tomasz