Re: [PATCH] usb: chipidea: Fix ULPI on imx51

[Nikita Yushchenko]

21.06.2018 17:12, Nikita Yushchenko wrote:
>>>> This patches causes a regression on a imx51-babbage running 4.18-rc1:
>>>> I get a kernel hang.
>>>>
>>>> If I revert it on top of 4.18-rc1, then it boots fine and USB host is
>>>> functional.
>>>>
>>>> I understand this patch fixes a kernel hang for you, so which commit
>>>> is responsible for the hang you observe?
>>>>
>>
>> I never assumed it was a regression and that USB worked on RDU1 board
>> before, so I never tried to see if this was a regression. I can only
>> tell you that it hangs as soon as any PORTSC registers are accessed.
> 
> Hang at register access usually means that module that owns the register
> is not clocked.

On RDU1, call to usb_phy_init() actually calls usb_gen_phy_init() that
does regulator_enable() for &vusb_reg and clk_prepare_enable() for
&clk_26M_usb.  I thing some of these two is actually needed to avoid
hang on register access.