linux-kernel - Re: [PATCH v6] i2c-gpio: add devicetree support

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Message-ID: <4D670E4B.6000407@wytron.com.tw>
Date:	Fri, 25 Feb 2011 10:04:59 +0800
From:	Thomas Chou <thomas@...ron.com.tw>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	Ben Dooks <ben-linux@...ff.org>, linux-kernel@...r.kernel.org,
	nios2-dev@...c.et.ntust.edu.tw,
	devicetree-discuss@...ts.ozlabs.org, linux-i2c@...r.kernel.org,
	Albert Herranz <albert_herranz@...oo.es>
Subject: Re: [PATCH v6] i2c-gpio: add devicetree support

Hi Grant,

On 02/25/2011 12:22 AM, Grant Likely wrote:
>> +Required properties:
>> +- compatible : should be "i2c-gpio".
>> +- gpios : should specify GPIOs used for SDA and SCL lines, in that order.
>> +Optional properties:
>> +- sda-is-open-drain : present if SDA gpio is open-drain.
>> +- scl-is-open-drain : present if SCL gpio is open-drain.
>> +- scl-is-output-only : present if the output driver for SCL cannot be
>> +	turned off. this will prevent clock stretching from working.
>> +- speed-hz : SCL frequency.
>
> Hi Thomas,
>
> One nitpick; I just looked, and other i2c controllers are already
> using 'clock-frequency' instead of 'speed-hz' for the speed of the
> bus.  I'd like to see this patch use the same terminology.

I studied 'clock-frequency' usage of existing i2c drivers before working 
on this patch.

i2c-ibm_iic.c, i2c-mpc.c, i2c-ocores.c : use as bus clock frequency 
input to the core.

i2c-cpm.c : use as i2c SCL output frequency.

Most other non-i2c drivers use clock-frequency as bus clock frequency 
input, too.

I think the SCL freq usage in i2c-cpm.c is confusing. So I would suggest 
we borrow 'speed-hz' from spi subsystem, which means the clock freq 
output on the peripheral bus.

Best regards,
Thomas

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