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

From: Grant Likely <grant.likely@arm.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Saravana Kannan <saravanak@google.com>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Artem Bityutskiy <artem.bityutskiy@linux.intel.com>,
	Felipe Balbi <balbi@kernel.org>, Mark Brown <broonie@kernel.org>,
	Ferry Toth <fntoth@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>, nd <nd@arm.com>
Subject: Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied
Date: Thu, 26 Mar 2020 13:45:50 +0000	[thread overview]
Message-ID: <6c04af00-adc8-6be2-b7fd-b4a875524563@arm.com> (raw)
In-Reply-To: <20200326120323.GR1922688@smile.fi.intel.com>

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@google.com> wrote:
>>>> On Wed, Mar 25, 2020 at 5:51 AM Andy Shevchenko
>>>> <andriy.shevchenko@linux.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.