linux-kernel - Re: [PATCH] i2c: designware: use enable on resume instead initialization

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Date:	Wed, 24 Jun 2015 16:06:45 +0200
From:	christian.ruppert@...tech.com
To:	"De Marchi, Lucas" <lucas.demarchi@...el.com>
Cc:	"christian.ruppert@...lis.com" <christian.ruppert@...lis.com>,
	"Mello, Fabio" <fabio.mello@...el.com>,
	"jarkko.nikula@...ux.intel.com" <jarkko.nikula@...ux.intel.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lucas.de.marchi@...il.com" <lucas.de.marchi@...il.com>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	"wsa@...-dreams.de" <wsa@...-dreams.de>
Subject: Re: [PATCH] i2c: designware: use enable on resume instead initialization

Dear Lucas,

"De Marchi, Lucas" <lucas.demarchi@...el.com> wrote on 24.06.2015 
14:56:19:
> On Wed, 2015-06-24 at 14:27 +0300, Mika Westerberg wrote:
> > On Wed, Jun 24, 2015 at 09:36:43AM +0200, 
christian.ruppert@...tech.com wrot
> > e:
> > > Dear Lucas,
> > > 
> > > Lucas De Marchi <lucas.de.marchi@...il.com> wrote on 23.06.2015 
19:02:03:
> > > > On Tue, Jun 23, 2015 at 1:45 PM,  <christian.ruppert@...tech.com> 
wrote:
> > > > > Hello,
> > > > > 
> > > > > Christian Ruppert/ALi_GVA/ALi wrote on 10.06.2015 17:05:16:
> > > > [...]
> > > > > The result is not very encouraging: Out of five (identical) 
> designware 
> > > > > 
> > > i2c
> > > > > controllers we have on my test SOC, the first one 
> initialises properly 
> > > > > 
> > > but
> > > > > the second one gets stuck in the famous irq loop right away when 
the
> > > > > module is enabled in i2c_dw_init. The system never gets around 
to try
> > > > 
> > > > Are you using the pci or platform driver?  I noticed yesterday the 
pci
> > > > version is failing here with a NULL pointer dereference.
> > > 
> > > The test was performed with the platform driver (instantiated 
through 
> > > device tree).
> > > I just re-checked and the ultimate problem which hangs/kills 
thesystem in 
> > > 
> > > my case is the IRQ loop.
> > > I haven't observed any NULL pointer dereferences on the road.
> > 
> > Thanks Christian for testing.
> > 
> > Since the patch causes problems on your hardware, I don't think it is
> > good idea to merge it.
> 
> 
> Yeah, but it would be bad to ignore the problem as well. The way it is 
now
> kills any possibility of using DW controller for reading sensors like
> gyroscope, accelerometer, barometer that have higher sampling rate etc. 
I'll
> try to come up with a new patch but since I can't reproduce the problem 
here
> it'd be good to know if there's any means for me to test.

I'll analyse the problem a bit further and send you a description (sda and 
scl state at enable time) as soon as I can put my hands on an oscilloscope 
one evening.

Greetings,
  Christian

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