[PATCH 1/2] fixup! usb: dwc2: Add support for optional usb phy

Ahmad Fatoum a.fatoum at pengutronix.de
Tue Mar 22 01:25:12 PDT 2022

Hello Michael,

On 22.03.22 09:19, Michael Grzeschik wrote:
> On Tue, Mar 22, 2022 at 06:35:22AM +0100, Ahmad Fatoum wrote:
>> On 21.03.22 23:17, Michael Grzeschik wrote:
>>> On Wed, Jan 06, 2021 at 11:05:43AM +0100, Sascha Hauer wrote:
>>>> On Mon, Dec 21, 2020 at 01:32:50AM +0100, Ahmad Fatoum wrote:
>>>>> Linux doesn't seem to enforce a fixed order between phy_init and
>>>>> phy_power_on. The Linux dwc2 driver does power_on and then phy_init,
>>>>> which is the inverse of what barebox is currently doing.
>>>>> The PHYs normally used with dwc2 are written with this in mind.
>>>>> For example, our stm32-usbphyc driver fails to disable:
>>>>>   ERROR: stm32-usbphyc 5a006000.usbphyc at 5a006000.of: PLL not reset
>>>>>   ERROR: phy1: phy exit failed --> -5
>>>>> Because Linux does exit -> power_off, but barebox does power_off ->
>>>>> exit.
>>>>> Issue was raised upstream:
>>>>> https://lore.kernel.org/lkml/6cd01e79-fdc0-3bd4-32b5-a85142533f8a@pengutronix.de/T/#t
>>>>> Until this is settled, swap the order to follow what Linux does.
>>>>> This is suboptimal, because it means controller drivers have different
>>>>> order of the operations and that you can't combine arbitrary PHYs and
>>>>> controllers, but it seems unlikely we will support combinations that
>>>>> aren't supported by Linux in the first place anyway.
>>>> This is valuable information and I don't want it to be lost, so instead
>>>> of applying this as a fixup I rewrote the subject to:
>>>> usb: dwc2: swap order of phy_init and phy_power_on to what Linux does
>>>> and applied it as a separate patch.
>>> With this patch applied, some stm32mp1 do seem to timeout when
>>> addressing the core.
>>> WARNING: dwc2 49000000.usb-otg at 49000000.of: dwc2_core_reset: Timeout! Waiting for Core Soft Reset
>>> ERROR: dwc2 49000000.usb-otg at 49000000.of: probe failed: Connection timed out
>>> When I revert this patch. Everything works fine again.
>>> Is it possible that we can revert it in mainline now?
>> Since 0e37f94fbe1b ("phy: stm32: sync with upstream"), the phy-stm32-usbphyc now
>> has no poweron/poweroff callbacks, so a revert seems to only slightly change
>> timing. I'd suggest you dig some more.
> That is not true. phy_power_on also enables the phy_regulator. Changing
> this order has the effect that the regulator is enabled after or before
> phy_init call.

Oh, good point. 

>>> How can I reproduce the case this was fixing in the first place?
>> The case was that barebox calls poweron/init in a different order than Linux.
>> This point is moot now though because poweron is no longer provided by the
>> driver.
> Still not true, though.

Isn't this the same order Linux uses? Powering on regulator and then phy_init?
Why does it lead to issues in barebox, but not in Linux?


> Regards,
> Michael

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