+Rafael, Kevin and Ulf,
On Tue, May 9, 2017 at 8:16 PM, Sakari Ailus <sakari.ailus@xxxxxx> wrote:
> Hi Tomasz,
>
> On Tue, May 09, 2017 at 07:38:26PM +0800, Tomasz Figa wrote:
>> On Tue, May 9, 2017 at 6:40 PM, Sakari Ailus <sakari.ailus@xxxxxx> 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@xxxxxx> wrote:
>> >> > Hi Rajmohan,
>> >> >
>> >> > A few comments below...
>> >> >
>> >> > On Sun, May 07, 2017 at 04:33:24AM -0700, rajmohan.mani@xxxxxxxxx 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.
>
> I have to admit I'm no expert in the topic but I'd presume that other
> implementations should still maintain consistent behaviour towards drivers.
> acpi_subsys_runtime_resume() is the PM domain runtime_resume() callback in
> acpi_general_pm_domain.
Let's see. For platform bus this seems to be reasonable indeed -
__rpm_get_callback() will use the callbacks of PM domain, device type,
device class or device bus, whichever is available first, in this
order. Looking at platform_bus_type, the equivalent resume callback is
pm_generic_runtime_resume() and it will indeed silently return 0 if
there is no dev->pm->runtime_resume.
However for I2C bus, i2c_bus_type doesn't seem to have .pm defined.
Type and class are device/driver-specific things, so let's assume they
don't have .pm set. If the driver doesn't have .pm, then the only way
__rpm_get_callback() can return a non-NULL value is when
dev->pm_domain is non NULL (which seems to be the ACPI case actually).
Otherwise, if __rpm_get_callback() returns NULL, pm_runtime_get*()
will fail with -ENOSYS. This is because rpm_resume() calls
rpm_callback(callback, dev), where callback is the value returned by
__rpm_get_callback() and rpm_callback() returns -ENOSYS if callback is
NULL. This is where pm_runtime_no_callbacks() comes handy, as it
bypasses the code getting and calling the callback, so it doesn't
return the error anymore.
There is however the other side of the coin. If
pm_runtime_no_callbacks() is called, all kind of callbacks are
bypassed, so even the PM domain code is not invoked. This is kind of
tricky, because the driver must be now aware of whether it's running
under a PM domain or not and call this pm_runtime_no_callbacks()
depending on the outcome, to guarantee correct operation (PM domain
callbacks must be called, even if device driver doesn't have its
own)... Which IMHO doesn't make sense.
I guess the correct way to proceed here would be adding .pm ops to
i2c_bus_type, just as it's done with platform_bus_type.
>
>>
>> >
>> >>
>> >> >
>> >> >> +}
>> >> >> +
>> >> >> +/* 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.
>
> No harm done. Very good comments in general IMO, thanks for those!
>
> --
> Kind regards,
>
> Sakari Ailus
> e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx
