linux-kernel - RE: [PATCH 1/1] I2C: designware: fix IO timeout issue for AMD controller

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Date:	Fri, 6 Nov 2015 09:11:35 +0000
From:	"Yu, Xiangliang" <Xiangliang.Yu@....com>
To:	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
CC:	"andriy.shevchenko@...ux.intel.com" 
	<andriy.shevchenko@...ux.intel.com>,
	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Xue, Ken" <Ken.Xue@....com>, "Wan, Vincent" <Vincent.Wan@....com>,
	"Huang, Ray" <Ray.Huang@....com>,
	"Wang, Annie" <Annie.Wang@....com>, "Li, Tony" <Tony.Li@....com>
Subject: RE: [PATCH 1/1] I2C: designware: fix IO timeout issue for AMD
 controller

> -----Original Message-----
> From: Jarkko Nikula [mailto:jarkko.nikula@...ux.intel.com]
> Sent: Friday, November 06, 2015 5:00 PM
> To: Yu, Xiangliang; Mika Westerberg
> Cc: andriy.shevchenko@...ux.intel.com; wsa@...-dreams.de; linux-
> i2c@...r.kernel.org; linux-kernel@...r.kernel.org; Xue, Ken; Wan, Vincent;
> Huang, Ray; Wang, Annie; Li, Tony
> Subject: Re: [PATCH 1/1] I2C: designware: fix IO timeout issue for AMD
> controller
> 
> On 06.11.2015 06:34, Yu, Xiangliang wrote:
> >> -----Original Message-----
> >> From: Mika Westerberg [mailto:mika.westerberg@...ux.intel.com]
> >>> --- a/drivers/i2c/busses/i2c-designware-core.c
> >>> +++ b/drivers/i2c/busses/i2c-designware-core.c
> >>> @@ -783,6 +783,9 @@ irqreturn_t i2c_dw_isr(int this_irq, void
> >>> *dev_id)
> >>>
> >>>   	stat = i2c_dw_read_clear_intrbits(dev);
> >>
> >> What if the status changes right here, before you go and mask the
> interrupt?
> > Have no effect, because i2c controller can't trigger next interrupt.
> >
> Does it mean possible lost interrupt too? I guess it can be debugged by
> placing a few ms long mdelay() between clearing and masking.
> 

The interrupt will not be lost if status bits change before masking interrupt.

> How frequent is this timeout? I guess lost interrupt is somehow nearly
> related to clearing, masking and unmasking if that cycle helps. One thing that
> comes to my mind is masking needed and could plain unmasking be also a
> working workaround?

Quite frequently.

> 
> Have you tried to print DW_IC_INTR_STAT, DW_IC_INTR_MASK and
> DW_IC_RAW_INTR_STAT when timeout occurs? E.g. just after printing the
> timeout out error in i2c_dw_xfer(). Probably good in i2c_dw_isr() too if if
> doesn't produce too much data and make debugging impossible.
> 

Yes, I have tried to print these status. I have confirmed the issue with hardware engineer. 
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