Re: About a suspicious msleep during doxfer in s3c2410 i2c bus driver

[Mark Brown <broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>]

On Wed, Jul 22, 2009 at 05:12:17PM +0900, Dongsoo, Nathaniel Kim wrote:

> Since I was working on S3C64XX and C1XX, I found something weird on
> I2C bus device.
> The thing is that when I try to write multiple registers through I2C
> bus, it takes much more time for multiple registers to be written than
> any other processor's i2c bus device.

Yes, this is extremely painful for a lot of devices - audio CODECs tend
to be noticably affected, especially at resume.  Depending on your
device and what you're doing you *may* be able to speed things up by
accessing many registers in a single I/O in the chip driver but
obviously that's not ideal.

> With several different target boards using s3c64xx and s5pc1xx, it
> went good without that msleep(). And of course it is working great
> with multiple i2c device attached as well.
> So, I want to ask Ben and anyone else using I2C device about removing
> that msleep might be ok or not. In my case, it went ok. Please let me
> know your opinion.

My *recollection* is that this is mostly there for multi-master
configurations.

I'm wondering if even if we can't remove the delay completely yet we
could add platform data to allow it to be configured on a per-board
basis?