linux-kernel - Re: [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C

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Message-ID: <CAFcVECKMqACtumHZGHbToUUSjd_dWCcLbu=_ZjNnnGdAZQ_3fg@mail.gmail.com>
Date:	Tue, 2 Dec 2014 19:00:40 +0530
From:	Harini Katakam <harinikatakamlinux@...il.com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	Mark Rutland <mark.rutland@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"michal.simek@...inx.com" <michal.simek@...inx.com>,
	"soren.brinkmann@...inx.com" <soren.brinkmann@...inx.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"vishnum@...inx.com" <vishnum@...inx.com>
Subject: Re: [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start
 property for Cadence I2C

Hi,

On Tue, Dec 2, 2014 at 6:46 PM, Wolfram Sang <wsa@...-dreams.de> wrote:
>
>> But given the bugs, it will be useful to just disable it if the system doesn't
>> require repeated start.
>
> What do you do when disable repeated start? Sending STOP and START? If
> so, this is really something different than repeated start. By using
> I2C_FUNC_I2C a user expects repeated start, so if the HW does not
> support it, we should say so and don't try to emulate it with something
> different.
>

Yes, we send stop.
Using repeated start, when number of messages passed > 1, HOLD bit is set
by the driver. This is an indication to the controller not to send a STOP.
If we disable repeated start, the driver will not set HOLD bit.
All the messages are sent but with START and a STOP for each of them.

Regards,
Harini
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