linux-kernel - Re: [PATCH v3 1/4] i2c: tegra: implement slave mode

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Message-ID: <20150724105251.GA22787@katana>
Date:	Fri, 24 Jul 2015 12:52:51 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Andrey Danin <danindrey@...l.ru>
Cc:	Stephen Warren <swarren@...dotorg.org>, devicetree@...r.kernel.org,
	devel@...uxdriverproject.org, linux-i2c@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, ac100@...ts.launchpad.net,
	Laxman Dewangan <ldewangan@...dia.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Julian Andres Klode <jak@...-linux.org>,
	Marc Dietrich <marvin24@....de>
Subject: Re: [PATCH v3 1/4] i2c: tegra: implement slave mode


> At the begin of my work on this patchset I even denied clock disable call if
> slave is registered (to minimize code that can affect transfer).

I hacked something like this, but it seems it was not enough.

> If only slave mode is used, then this logic is not needed.

This is not sufficent. We shouldn't break being a master only because we
also listen to a slave address (as long as the HW supports that of
course).

> tegra_i2c_init is called on probe and resume. Also it is called in case of
> xfer fail. If xfer is ok, then I think slave addr must be kept unchanged.

This is fragile. Try scanning the bus with i2cdetect and slave setup
will be gone.

> As far as I understand it is a loopback mode. Probably it will not work
> (Stephen Warren already mentioned this).

Just to make clear: I am not saying we should support talking to our own
slave address. But it should still be possible to communicate with other
remote devices on the bus.

Thanks,

   Wolfram

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