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

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Date:	Fri, 24 Jul 2015 13:18:28 +0300
From:	Andrey Danin <danindrey@...l.ru>
To:	Wolfram Sang <wsa@...-dreams.de>,
	Stephen Warren <swarren@...dotorg.org>
Cc:	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

On 24.07.2015 12:27, Wolfram Sang wrote:
> Still doesn't work for me and I think I understand why. Do you run your
> I2C controller in slave mode only?

Yes.

> That might work, but using it in
> master/slave mode simultanously won't work yet as I see it:
>
> * After every transfer (as master), clocks get disabled. I assume the IP
>    core won't be able to detect its own address then.

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

>
> * There is this code in tegra_i2c_init():
>
> 	if (!i2c_dev->is_dvc) {
> 		u32 sl_cfg = i2c_readl(i2c_dev, I2C_SL_CNFG);
> 		sl_cfg |= I2C_SL_CNFG_NACK | I2C_SL_CNFG_NEWSL;
> 		i2c_writel(i2c_dev, sl_cfg, I2C_SL_CNFG);
> 		i2c_writel(i2c_dev, 0xfc, I2C_SL_ADDR1);
> 		i2c_writel(i2c_dev, 0x00, I2C_SL_ADDR2);
>
> 	}
>
>    It probably messes up the slave initialization in tegra_reg_slave().
>    At least I see that the slave address gets overwritten when I peek
>    the register after boot.
>

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.

> Does that make sense to you?

As far as I understand it is a loopback mode. Probably it will not work 
(Stephen Warren already mentioned this).
But we can try to run it.

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