Re: [PATCH 4/7] phy: meson: add USB2 PHY support for Meson8b and GXBB

Ben Dooks
2016-09-08T20:20:12Z

On 08/09/16 20:52, Martin Blumenstingl wrote:
> On Thu, Sep 8, 2016 at 9:35 PM, Kevin Hilman <khilman-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> wrote:
>>> + phy = devm_phy_create(&pdev->dev, NULL, &phy_meson_usb2_ops);
>>> + if (IS_ERR(phy)) {
>>> + dev_err(&pdev->dev, "failed to create PHY\n");
>>> + return PTR_ERR(phy);
>>> + }
>>> +
>>> + if (usb_reset_refcnt++ == 0) {
>>> + ret = device_reset(&pdev->dev);
>>> + if (ret) {
>>> + dev_err(&phy->dev, "Failed to reset USB PHY\n");
>>> + return ret;
>>> + }
>>> + }
>>
>> The ref count + reset here looks like something that could/should be
>> handled in a runtime PM callback.
> Unfortunately that doesn't work (as Jerome found out) because both
> PHYs are sharing the same reset line.
> So if the second PHY would call device_reset then it would also reset
> the first PHY!
>
> There's a comment above the declaration of usb_reset_refcnt which
> tries to explain this:
> "The PHYs are sharing a common reset line -> we are only allowed to
> reset once for all PHYs."
> Maybe I should move this comment to the "if (usb_reset_refcnt++ == 0)
> {" line to make it easier to see?
>

pm-runtime has refcounting in it. When one of the nodes turns on,
the pm-runtime will call your driver to say there is a user when
this first use turns up.

If all the sub-phys turn off and drop their refcount then the driver
is called to say there are no more users and you can go to sleep.

So, in phy_meson_usb2_power_on() you could do:

pm_runtime_get_sync(pdev);

and in phy_meson_usb2_power_off

pm_runtime_put(pdev);

https://www.kernel.org/doc/Documentation/power/runtime_pm.txt

--
Ben Dooks http://www.codethink.co.uk/
Senior Engineer Codethink - Providing Genius
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