linux-kernel - Re: [PATCH v2 6/7] i2c: ChromeOS EC tunnel driver

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Message-ID: <20140423123746.GG640@lee--X1>
Date:	Wed, 23 Apr 2014 13:37:46 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	swarren@...dia.com, wsa@...-dreams.de, 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: [PATCH v2 6/7] i2c: ChromeOS EC tunnel driver

On Tue, 22 Apr 2014, 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 original Samsung ARM Chromebook these devices were on an I2C
> bus that was shared between the AP and the EC and arbitrated using
> some extranal GPIOs (see i2c-arb-gpio-challenge).
> 
> The original arbitration scheme worked well enough but had some
> downsides:
> * It was nonstandard (not using standard I2C multimaster)
> * It only worked if the EC-AP communication was I2C
> * It was relatively hard to debug problems (hard to tell if i2c issues
>   were caused by the EC, the AP, or some device on the bus).
> 
> On the HP Chromebook 11 the design was changed to:
> * The AP/EC comms were still i2c, but the battery/tps65090 were no
>   longer on the bus used for AP/EC communication.  The battery was
>   exposed to the AP through a limited i2c tunnel and tps65090 was
>   exposed to the AP through a custom Linux driver.
> 
> 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.
> 
> The upstream "tegra124-venice2" uses the same scheme as the Samsung
> ARM Chromebook 2, though it has a different set of components on the
> other side of the bus.
> 
> 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).
> 
> Signed-off-by: Vincent Palatin <vpalatin@...omium.org>
> Signed-off-by: Simon Glass <sjg@...omium.org>
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> Tested-by: Andrew Bresticker <abrestic@...omium.org>
> Tested-by: Stephen Warren <swarren@...dia.com>
> ---
> Changes in v2:
> - Update tunnel binding as per swarren
> 
>  .../devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt |  39 +++
>  drivers/i2c/busses/Kconfig                         |   9 +
>  drivers/i2c/busses/Makefile                        |   1 +
>  drivers/i2c/busses/i2c-cros-ec-tunnel.c            | 304 +++++++++++++++++++++
>  drivers/mfd/cros_ec.c                              |   5 +

For the MFD changes:
  Acked-by: Lee Jones <lee.jones@...aro.org>

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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