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

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Date:	Tue, 20 Jan 2015 16:34:10 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
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

On Tue, 20 Jan 2015, Javier Martinez Canillas wrote:

> Hello Lee,
> 
> On 01/20/2015 09:11 AM, Lee Jones wrote:
> > On Fri, 02 Jan 2015, Javier Martinez Canillas wrote:
> > 
> >> From: Bill Richardson <wfrichar@...omium.org>
> >> 
> >> This adds the LPC interface to the Chrome OS EC. Like the
> >> I2C and SPI drivers, this allows userspace access to the EC.
> > 
> > I'm fairly certain that this is _not_ an MFD device.  Please locate it
> > to the proper subsystem (input?).
> > 
> 
> Sorry, it wasn't my intention to use the mfd subsystem as a place to dump
> random drivers. Is that I still find hard to understand what is the line
> between what falls under mfd and what doesn't.
> 
> For example, I see that mfd drivers are for devices which have multiple
> functions and the mfd driver is the one that spawns the platform devices
> and provide an interface to access the I/O registers used by the different
> platform drivers of the sub-devices.
> 
> 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.

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