linux-kernel - Re: [PATCH] usb: chipidea: Fix ULPI on imx51

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Message-ID: <26d9fd57-07bc-0bba-2f29-ca778bd85328@cogentembedded.com>
Date:   Thu, 21 Jun 2018 17:25:01 +0300
From:   Nikita Yushchenko <nikita.yoush@...entembedded.com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        Fabio Estevam <festevam@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Chen <peter.chen@....com>, linux-usb@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>
Subject: Re: [PATCH] usb: chipidea: Fix ULPI on imx51



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.