linux-kernel - Re: [RESEND PATCH 6/7] i2c: ChromeOS EC tunnel driver

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Message-ID: <53555AFC.5020203@wwwdotorg.org>
Date:	Mon, 21 Apr 2014 11:53:00 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Doug Anderson <dianders@...omium.org>, lee.jones@...aro.org,
	swarren@...dia.com, wsa@...-dreams.de
CC:	abrestic@...omium.org, dgreid@...omium.org, olof@...om.net,
	sjg@...omium.org, linux-samsung-soc@...r.kernel.org,
	linux-tegra@...r.kernel.org,
	Vincent Palatin <vpalatin@...omium.org>, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	rdunlap@...radead.org, sameo@...ux.intel.com, jdelvare@...e.de,
	shane.huang@....com, maxime.ripard@...e-electrons.com,
	laurent.pinchart+renesas@...asonboard.com,
	u.kleine-koenig@...gutronix.de, bjorn.andersson@...ymobile.com,
	kevin.strasser@...ux.intel.com, linux@...sktech.co.nz,
	andrew@...n.ch, andriy.shevchenko@...ux.intel.com,
	schwidefsky@...ibm.com, matt.porter@...aro.org,
	ch.naveen@...sung.com, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org
Subject: Re: [RESEND PATCH 6/7] i2c: ChromeOS EC tunnel driver

On 04/17/2014 12:36 PM, Doug Anderson wrote:
> On ARM Chromebooks we have a few devices that are accessed by both the
> AP (the main "Application Processor") and the EC (the Embedded
> Controller).  These are:
> * The battery (sbs-battery).
> * The power management unit tps65090.
...
> On the Samsung ARM Chromebook 2 the scheme is changed yet again, now:
> * The AP/EC comms are now using SPI for faster speeds.
> * The EC's i2c bus is exposed to the AP through a full i2c tunnel.
...
> This driver supports the scheme used by the Samsung ARM Chromebook 2.
> Future patches to this driver could add support for the battery tunnel
> on the HP Chromebook 11 (and perhaps could even be used to access
> tps65090 on the HP Chromebook 11 instead of using a special driver,
> but I haven't researched that enough).

> diff --git a/Documentation/devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt b/Documentation/devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt

> +I2C bus that tunnels through the ChromeOS EC (cros-ec)
> +======================================================
> +On some ChromeOS board designs we've got a connection to the EC (embedded
> +controller) but no direct connection to some devices on the other side of
> +the EC (like a battery and PMIC).  To get access to those devices we need
> +to tunnel our i2c commands through the EC.
> +
> +The node for this device should be under a cros-ec node like google,cros-ec-spi
> +or google,cros-ec-i2c.
> +
> +
> +Required properties:
> +- compatible: google,cros-ec-i2c-tunnel
> +- google,remote-bus: The EC bus we'd like to talk to.

It's probably worth mentioning here that the node represents a single
I2C bus, and hence is expected to contain child nodes representing I2C
devices. Perhaps:

Optional child nodes:
- One node per I2C device connected to the tunnelled I2C bus.

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