linux-kernel - Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied

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Message-ID: <6c04af00-adc8-6be2-b7fd-b4a875524563@arm.com>
Date:   Thu, 26 Mar 2020 13:45:50 +0000
From:   Grant Likely <grant.likely@....com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Felipe Balbi <balbi@...nel.org>,
        Mark Brown <broonie@...nel.org>, Ferry Toth <fntoth@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        nd <nd@....com>
Subject: Re: [PATCH v3] driver core: Break infinite loop when deferred probe
 can't be satisfied



On 26/03/2020 12:03, Andy Shevchenko wrote:
> On Thu, Mar 26, 2020 at 11:45:18AM +0200, Peter Ujfalusi wrote:
>> On 26/03/2020 10.39, Rafael J. Wysocki wrote:
>>> On Wed, Mar 25, 2020 at 11:09 PM Saravana Kannan <saravanak@...gle.com> wrote:
>>>> On Wed, Mar 25, 2020 at 5:51 AM Andy Shevchenko
>>>> <andriy.shevchenko@...ux.intel.com> wrote:
> 
> ...
> 
>>> OK, so the situation right now is that commit 58b116bce136 has
>>> introduced a regression and so it needs to be fixed or reverted.  The
>>> cases that were previously broken and were unbroken by that commit
>>> don't matter here, so you cannot argue that they would be "broken".
>>
>> commit 58b116bce136 is from 2014 and the whole ULPI support for dwc3
>> came in a year later.
>> While I agree that 58b116bce136 fail to handle came a year later, but
>> technically it did not introduced a regression.
>>
>> The revert on the other hand is going to introduce a regression as
>> things were working fine since 2014. Not sure why the dwc3 issue got
>> this long to be noticed as the 58b116bce136 was already in kernel when
>> the ULPI support was added...
> 
> I dare to say that is luck based on people's laziness to figure out the root
> cause. As I pointed out in email to Saravana the issue is not limited to USB
> case and, if my memory doesn't trick me out, I suffered from it approximately
> in ~2014-2015 with pin control tables.

I've not been involved in this for a very long time, but from our past 
conversations and the description that is given here I still feel that 
this problem is a design bug on the dwc3 driver dependencies rather than 
a failure with driver core. dwc3 is doing something rather convoluted 
and it would be worth reevaluating how probe failures are unwound on 
that particular driver stack.

g.