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

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Message-ID: <54C0BE21.7020008@collabora.co.uk>
Date:	Thu, 22 Jan 2015 10:08:49 +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 01/22/2015 09:42 AM, Lee Jones wrote:
>> > 
>> > 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.
> 
> I'm not sure that's true.  It's pretty simple I grant you, but it
> still looks like a driver, rather than an abstraction layer.
> 
> I would expect to see something more like:
> 
> static int cros_ec_lpc_readmem(...)
> {
> 	return call_to_driver_to_read_memory(...);
> 	
> }
> 
> ... instead of all those memory/register reads/writes.
>

Yeah... in that sense I've to admit that is more complex than the I2C and SPI
drivers, yet those have a subsystem in the kernel with helpers functions to
do most of the communication:

static int cros_ec_cmd_xfer_i2c(struct cros_ec_device *ec_dev,
				struct cros_ec_command *msg)
{
...
	ret = i2c_transfer(client->adapter, i2c_msg, 2);
...
}

static int cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev,
				struct cros_ec_command *ec_msg)
{
...
	spi_message_add_tail(&trans, &msg);
	ret = spi_sync(ec_spi->spi, &msg);
...
}

But there doesn't seem to be a LPC subsystem in the kernel so we don't have a
nice abstraction layer in this case.

> Are there any other Low Pin Count drivers in the kernel?
>

I don't know tbh, I didn't even know what LPC was before I picked this patch
to push it upstream. I searched in the Linux codebase for other LPC drivers
but I didn't find anything, that doesn't mean that it doesn't exist though.

Best regards,
Javier
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