linux-kernel - Re: [PATCH RESEND v2 3/7] mfd: cros_ec: Add cros_ec

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Date:	Tue, 20 Jan 2015 17:52:20 +0100
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Lee Jones <lee.jones@...aro.org>
CC:	Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	Jonathan Corbet <corbet@....net>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v2 3/7] mfd: cros_ec: Add cros_ec_lpc driver for
 x86 devices

Hello Lee,

On 01/20/2015 05:34 PM, Lee Jones wrote:
>> 
>> So, the Embedded Controller driver (drivers/mfd/cros_ec.c) falls into that
>> category and in fact has been in the mfd driver for a long time. Now, if
>> an mfd device support different type of buses (e.g: i2c, spi, etc) I see
>> that both the core driver and the driver for the transport method are
>> in the drivers/mfd directory. As an example:
>> 
>> drivers/mfd/arizona-{core,i2c,spi}.c
>> drivers/mfd/da9052-{core,i2c,spi}.c
>> drivers/mfd/mc13xxx-{core,i2c,spi}.c
>> drivers/mfd/tps65912-{core,i2c,spi}.c
>> drivers/mfd/wm831x-{core,i2c,spi,otp}.c
>> 
>> In the cros_ec case, we already have drivers/mfd/cros_ec_{i2c,spi}.c so
>> since the Low Pin Count is another transport method I thought that this
>> driver belonged to the drivers/mfd directory.
>> 
>> Now, all those drivers may be wrong and the buses don't belong to the mfd
>> subsystem but then I think we need to document that since it seems that is
>> the correct way to do it just by looking at the other drivers.
> 
> I don't think the drivers you mentioned above do anything practical.
> For instance, they are not SPI/IC2/etc drivers.  They should only
> offer some abstraction layers which are used to communicate with the
> device.  The driver you are submitting looks a lot more like a device
> driver, which should live somewhere else.  Don't ask me where though,
> I'm not even sure what a Low Pin Controller does.
> 

The driver added by $subject doesn't really do anything practical either.
LPC [0] is just another transport method like i2c or spi that is used on
x86 Chromebooks to access the Embedded Controller.

So the driver is really not that different than the cros_ec_{i2c,spi}.c
drivers.

Best regards,
Javier

[0]: http://en.wikipedia.org/wiki/Low_Pin_Count
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