From mboxrd@z Thu Jan  1 00:00:00 1970
From: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Subject: Re: [PATCH RESEND v2 5/7] mfd: cros_ec: Instantiate ChromeOS EC character
 device
Date: Wed, 21 Jan 2015 17:56:49 +0100
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To: Lee Jones <lee.jones@linaro.org>
Cc: Olof Johansson <olof@lixom.net>, Doug Anderson <dianders@chromium.org>, Bill Richardson <wfrichar@chromium.org>, Simon Glass <sjg@google.com>, Gwendal Grignou <gwendal@google.com>, Jonathan Corbet <corbet@lwn.net>, linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org
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Hello Lee,

On 01/20/2015 06:11 PM, Javier Martinez Canillas wrote:
>> 
>> But is it really a chardev?  Don't chardevs usually live in
>> drivers/char?  It probably uses a chardev node in /dev, but what does
>> it really do?  What information can/will userspace obtain from this
>> memory block?
>> 
> 
> Right, is a driver that register a chardev but mostly to expose an ioctl
> interface to send commands to the Embedded Controller from user-space.
> 
> The Application Processor communicates with Embedded Controller by sending
> commands over an interface. This can be either spi or i2c on ARM (depending
> on the Chromebook model) or LPC on x86 Chromebooks so the platform driver
> instantiated by the "cros-ec-dev" mfd cell is to allow user-space to send
> commands to the Embedded Controller (using the correct transport method).
> 
> So this chardev is used by the ectool binary in ChromeOS to communicate
> with the Embedded Controller.
> 

Just FYI, I'll rename it to "cros-ec-ctl" since as you said is not really
a chardev but that just happens to be the interface chosen to send the ioctl
commands to the driver.

Thanks a lot for your suggestion.

Best regards,
Javier