linux-kernel - Re: [PATCH] rtc-ds1307: True SMBus compatibility

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Message-ID: <20090107162709.755982c0@hyperion.delvare>
Date:	Wed, 7 Jan 2009 16:27:09 +0100
From:	Jean Delvare <khali@...ux-fr.org>
To:	"Ed Swierk" <eswierk@...stanetworks.com>
Cc:	linux-i2c@...r.kernel.org, "David Brownell" <david-b@...bell.net>,
	"Alessandro Zummo" <a.zummo@...ertech.it>,
	linux-kernel@...r.kernel.org,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"BARRE Sebastien" <sbarre@...lcc.com>
Subject: Re: [PATCH] rtc-ds1307: True SMBus compatibility

Hi Ed,

On Wed, 7 Jan 2009 07:22:12 -0800, Ed Swierk wrote:
> On Wed, Jan 7, 2009 at 5:24 AM, Jean Delvare <khali@...ux-fr.org> wrote:
> > Are you certain the nForce2 controllers can't do it? The i2c-nforce2
> > driver doesn't implement it, but this doesn't mean the hardware can't
> > do it. I don't have any datasheet for these chips, but I know their
> > SMBus implementation is very similar to those of the AMD 8111, and
> > i2c-amd8111 has support for I2C block reads and writes. I think it
> > would be worth giving it a try, by copying the i2c-amd8111
> > implementation into the i2c-nforce2 driver and seeing if it happens to
> > just work. If it works, that would be more elegant than your proposed
> > hack to the rtc-ds1307 driver.
> 
> I checked the datasheet and also tried every possible SMBus command
> value to try to discover any supported commands that the i2c-nforce2
> driver happens not to use, to no avail. The nVidia SMBus is pure
> SMBus.

Did you try 0x4a (as i2c-amd8111 is using)?

So, you have the datasheet... Is this something you would be allowed to
share with me?

> I could change the ds1307 driver to check whether the controller
> supports i2c block commands and fall back to emulation only if they
> are not available. Would that address your concerns?

Yes, that would. Same thing the eeprom or lm93 drivers are doing, to
only name a few of them. Should be fairly easy.

-- 
Jean Delvare
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