From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 6 Nov 2008 11:53:39 +1100 From: David Gibson To: Mike Ditto Subject: Re: [PATCH] i2c-cpm: Add flexibility for I2C clock frequency and filter. Message-ID: <20081106005339.GF28465@yookeroo.seuss> References: <490A84F8.20403@consentry.com> <490AEEBF.9000707@scram.de> <20081105233617.GC28465@yookeroo.seuss> <49123BB7.90503@consentry.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <49123BB7.90503@consentry.com> Cc: linuxppc-dev@ozlabs.org, i2c@lm-sensors.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson