linux-kernel - Re: [PATCH 2/3] mfd: cros_ec: Create sysfs attributes for the ChromeOS EC.

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Date:	Thu, 20 Nov 2014 12:58:59 +0100
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Lee Jones <lee.jones@...aro.org>
CC:	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Olof Johansson <olof@...om.net>, Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mfd: cros_ec: Create sysfs attributes for the ChromeOS
 EC.

Hello Lee,

On 11/18/2014 03:26 PM, Lee Jones wrote:
> On Mon, 17 Nov 2014, Javier Martinez Canillas wrote:
> 
>> From: Bill Richardson <wfrichar@...omium.org>
>> 
>> This adds the first few sysfs attributes for the Chrome OS EC. These
>> controls are made available under /sys/devices/virtual/chromeos/cros_ec
>> 
>>     flashinfo   - display current flash info
> 
> drivers/mtd?
> 
>>     reboot      - tell the EC to reboot in various ways
> 
> drivers/power?
>

Well this driver is special in the sense that there is a Cortex-M Embedded
Controller that has different peripherals (flash, keyboard, charger, etc).
The kernel communicates with these peripherals by using a tunnel through
the protocol used to communicate with the Embedded Controller (SPI/I2C/LPC).

But you are right that this is not suitable for drivers/mfd, I just added
there because that is the location in the downstream ChromeOS kernel but
like you said, the MFD subsystem should not be a dumping ground for devices
that is not clear where should live.

On v2 I'll add this sysfs interface and the dev to drivers/platform/chrome/
since I think is a better place for the cros_ec dev driver. It will still
be spawns from the cros_ec MFD driver though but that is OK for you AFAIU.

>>     version     - information about the EC software and hardware
> 
> What's the difference between this version and the version you can
> read in the new _dev driver?
>

The version information read from the cros_ec dev interface is a subset
of the information read from the version sysfs, e.g:

$ cat /dev/cros_ec
1.0.0
pit_v1.1.1198-1cd618e
pit_v1.1.1198-1cd618e
read-only

$ cat /sys/class/chromeos/cros_ec/version
RO version:    pit_v1.1.1198-1cd618e
RW version:    pit_v1.1.1198-1cd618e
Firmware copy: RO
Build info:    pit_v1.1.1198-1cd618e 2014-04-30 16:29:52 @build122-m2
Chip vendor:   stm
Chip name:     stm32l15x
Chip revision:
Board version: 0

I don't really know why there are two interfaces for this but I guess
that different user-space utilities use one or another. Maybe the
ChromiumOS folks can comment on this.

Best regards,
Javier
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