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

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Date:	Tue, 2 Dec 2014 14:16:11 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Harini Katakam <harinikatakamlinux@...il.com>
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


> 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.

> If you think DT entry is not the way to go, do you think a CONFIG option or
> something better will work?

No, check at runtime if the transfer is possible on this HW. Bail out if
not.

> We chose a DT property because there is a good chance the user has multiple
> cadence I2C controllers - one connected to a slave that needs repeated start
> (like a power controller) and another that doesn't care.

The user should not need to know with this level of detail if we can
avoid it IMO.


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