linux-kernel - Re: [4/5] i2c: davinci: use bus recovery infrastructure

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Message-ID: <547331F2.3000006@ti.com>
Date:	Mon, 24 Nov 2014 15:26:10 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
CC:	Wolfram Sang <wsa@...-dreams.de>, <linux-i2c@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Sekhar Nori <nsekhar@...com>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Murali Karicheri <m-karicheri2@...com>
Subject: Re: [4/5] i2c: davinci: use bus recovery infrastructure

Hi Uwe,

On 11/23/2014 10:36 PM, Uwe Kleine-König wrote:
> On Fri, Nov 21, 2014 at 09:33:22PM +0200, Grygorii Strashko wrote:
>> On 11/21/2014 09:07 PM, Uwe Kleine-König wrote:
>>> On Thu, Nov 20, 2014 at 12:03:07PM +0200, Grygorii Strashko wrote:
>>> Just another general comment about the driver that doesn't influence the
>>> correctness of this patch: The i2c-davinci driver is quite quick to
>>> reset the bus. I wonder how often this reset triggers. Is the bus in
>>> question less "stable" than others?
>>
>> In comparison to ..? :)
> In comparison to other bus drivers in other SoCs. I know this might be
> hard to answer. I just wonder where the reason for this has to be
> located. Strange hardware? Software bug? Or is this SoC just operating
> with strange slaves more often than others?

Davinci driver does reset in two cases:
- when I2C transaction isn't completed due to timeout (no irq received)
- when BB is detected
both cases are reasonable, because in 1st case HW state is undefined
in 2d case - Davinci I2C supports only master mode and if BB detected
we need perform some recovery procedure.

Also, this patch doesn't introduce functional changes - it's just code
reworking intended to reuse I2C bus recovery infrastructure

i2c-omap.c - OMAP I2C driver does mostly the same now.
i2c-tegra.c - seems, It will do reset even frequently.
i2c-imx.c - if understand right, it will reinitialize I2C controller 
before each transfer, because it enables/disables I2C clocks.
... 

So, what i can say here is just "In comparison to ..?" :)

regards,
-grygorii
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