[PATCH] i2c-cpm: Add flexibility for I2C clock frequency and filter.

[David Gibson]

On Wed, Nov 05, 2008 at 04:35:03PM -0800, Mike Ditto wrote:
> David Gibson wrote:
> > What does worry me, however, is the description says it's about
> > whether the driver "should" enable the filter.  Generally the device
> > tree doesn't attempt to say what users "should" do with the hardware,
> > just what the characteristics of the hardware are.
> >
> > What's the underlying difference here that affects the driver's choice
> > to enable the filter or not?
> 
> I think it's a hardware/environment design parameter - e.g. if the I2C
> bus has hot-pluggable devices, long PCB traces, or a hierarchy of
> multiplexed bus segments, these can result in a noisy SCL signal that
> needs to be filtered.  It's also a recommended mitigation for errata
> in certain CPU revs.

Ah, ok.  Well the CPU revision thing could be selected based on the
CPU revision, but the other conditions are a property of the board
wiring.  Obviously it's hard to precisely characterize what it says
about the hardware, which is usually best avoided for devtree
properties, but I can see why this is more-or-less unavoidable in this
case.

Ok.  This property name and meaning looks ok to me.  I would suggest a
note in the binding roughly explaining what leads to the property
being set (basically what you just told me in the paragraph above).

-- 
David Gibson			| I'll have my music baroque, and my code
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				| _way_ _around_!
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