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

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Message-ID: <CAKi4VAJwD45VbWuCHegfkB-tbgvgza52-cgVNF4AxF8NCuYyRQ@mail.gmail.com>
Date:	Tue, 9 Jun 2015 15:29:01 -0300
From:	Lucas De Marchi <lucas.de.marchi@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-i2c@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Fabio Mello <fabio.mello@...el.com>,
	Lucas De Marchi <lucas.demarchi@...el.com>,
	Christian Ruppert <christian.ruppert@...lis.com>
Subject: Re: [PATCH] i2c: designware: use enable on resume instead initialization

Hi Mika,

On Tue, Jun 9, 2015 at 5:51 AM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> On Mon, Jun 08, 2015 at 02:50:28PM -0300, lucas.de.marchi@...il.com wrote:
>> From: Fabio Mello <fabio.mello@...el.com>
>>
>> According to documentation and tests, initialization is not
>> necessary on module resume, since the controller keeps its state
>> between disable/enable. Change the target address is also allowed.
>>
>> So, this patch replaces the initialization on module resume with a
>> simple enable, and removes the (non required anymore) enables and
>> disables.
>>
>> Signed-off-by: Fabio Mello <fabio.mello@...el.com>
>> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
>> ---
>>
>> These pictures explain a little more the consequence of letting the
>> enable+disable in the code:
>>
>>       http://pub.politreco.com/paste/TEK0011-before.jpg
>>       http://pub.politreco.com/paste/TEK0007-after.jpg
>>
>> The yellow line is a GPIO toggle in userspace to mark when we start and finish
>> the i2c transactions.  The blue line is the SCL in that i2c bus. Take a look on
>> the huge pauses we have between any 2 transactions.  These pauses are removed
>> with this patch and we are able to read our sensor's values in 950usec rather
>> than 5.24msec we had before.  We are testing this using a Minnowboard Max that
>> has a designware i2c controller.
>
> Did you test this on any other platform than Intel Baytrail?

No. The only soc we have here with this controller is the Baytrail.

-- 
Lucas De Marchi
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