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

Ben Dooks
2016-09-08T20:53:24Z

On 08/09/16 21:42, Kevin Hilman wrote:
> Ben Dooks <ben.dooks@codethink.co.uk> writes:
>
>> On 08/09/16 20:52, Martin Blumenstingl wrote:
>>> On Thu, Sep 8, 2016 at 9:35 PM, Kevin Hilman <khilman@baylibre.com> 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.
>
> After a chat w/Martin on IRC, It turns out runtime PM wont help here.
>
> The reason is because there are physically two PHY devices[1]. Those 2
> devices will be treated independely by runtime PM, and have separate
> use-counting, which means doing what I proposed would cause a reset to
> happen when either device was probed.
>
> So, I think it's OK as it is.

Surely you can do pm_runtime_get/put on the phy's parent platform
device and do it that way?

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