From mboxrd@z Thu Jan  1 00:00:00 1970
From: plagnioj@jcrosoft.com (Jean-Christophe PLAGNIOL-VILLARD)
Date: Wed, 22 Sep 2010 16:34:06 +0200
Subject: [PATCH] at91sam9g45: fix i2c bus speed
In-Reply-To: <87lj6uavde.fsf@macbook.be.48ers.dk>
References: <1285147886-17100-1-git-send-email-jacmet@sunsite.dk>
	<20100922104846.GQ32018@game.jcrosoft.org>
	<87lj6uavde.fsf@macbook.be.48ers.dk>
Message-ID: <20100922143406.GT32018@game.jcrosoft.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 13:08 Wed 22 Sep     , Peter Korsgaard wrote:
> >>>>> "Jean-Christophe" == Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com> writes:
> 
> Hi,
> 
>  >> Use a correct udelay value to get bus speed around 100KHz. The udelay
>  >> value was most likely copied from the older devices, but the 9g45
>  >> is signicantly faster (400MHz, DDR, ..), so a udelay of 2 gives a
>  >> bus speed of around 190KHz, which is too fast for some devices.
>  >> A udelay value of 5 gives a bus speed of around 90KHz here.
>  >> 
>  >> Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
> 
>  Jean-Christophe> in this case it will be better to overwite it at board
>  Jean-Christophe> than force it for all of them
> 
> You don't expect most 9g45 users will run at 400MHz? It seems pretty
> likely to me. In any case, a safe (but somewhat slow) default seems
> better than a potentially unsafe one.
> 
> Now, I agree that it would be nice to add an interface to tweak this
> delay if needed (extra argument to at91_add_device_i2c()?), but that's
> next to the discussion about what the default should be.
I'd prefer to calculate it

so we specify which max freq we want in my mind it will be good to be as in
spi to specific per device it's max speed so we can adapt the bus freq

Best Regards,
J.