linux-kernel - Re: [i2c] [PATCH6/7] i2c: adds support for i2c bus on Freescale CPM1/CPM2 controllers

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Date:	Tue, 06 May 2008 17:19:39 +0200
From:	Jochen Friedrich <jochen@...am.de>
To:	Wolfram Sang <w.sang@...gutronix.de>
CC:	Kumar Gala <galak@...nel.crashing.org>,
	linuxppc-dev list <linuxppc-dev@...abs.org>,
	"Kernel, Linux" <linux-kernel@...r.kernel.org>,
	Scott Wood <scottwood@...escale.com>,
	Linux I2C <i2c@...sensors.org>
Subject: Re: [i2c] [PATCH6/7] i2c: adds support for i2c bus on Freescale	CPM1/CPM2
 controllers

Hi Wolfram,

>> +	/* Begin transmission */
>> +	setbits8(&i2c_reg->i2com, 0x80);
> Hardcoded value. (I also wonder if 0x81 might be more suitable, as it
> keeps the "be-a-master"-bit set. Still, both values work with my setup.)

>> +#ifdef I2C_CHIP_ERRATA
>> +	/*
>> +	 * Chip errata, clear enable. This is not needed on rev D4 CPUs.
>> +	 * Disabling I2C too early may cause too short stop condition
>> +	 */
>> +	udelay(4);
>> +	clrbits8(&i2c_reg->i2mod, 1);
> I was unable to find the corresponding errata document, still I wonder
> if it is a 0 which should have been written? The text says "clear" and
> according to the reference manual, this means the bit should be 0.

setbits8() and clrbits8() use a bitmask as second argument.

setbits8(&i2c_reg->i2com, 0x80) will set bit 7 on the i2com register but 
leave bit 0 untouched. Likewise, clrbits8(&i2c_reg->i2mod, 1) will clear bit 0.

Thanks,
Jochen
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