From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Grant Likely" Subject: Re: [PATCH 3/4] spi: Add OF binding support for SPI busses Date: Mon, 19 May 2008 09:57:21 -0600 Message-ID: References: <20080516193054.28030.35126.stgit@trillian.secretlab.ca> <20080516193613.28030.13950.stgit@trillian.secretlab.ca> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: fabrizio.garetto@gmail.com, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, dbrownell@users.sourceforge.net, spi-devel-general@lists.sourceforge.net To: "Guennadi Liakhovetski" Return-path: In-Reply-To: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linuxppc-dev-bounces+glppd-linuxppc64-dev=m.gmane.org@ozlabs.org Errors-To: linuxppc-dev-bounces+glppd-linuxppc64-dev=m.gmane.org@ozlabs.org List-Id: linux-spi.vger.kernel.org On Mon, May 19, 2008 at 7:17 AM, Guennadi Liakhovetski wrote: > On Fri, 16 May 2008, Grant Likely wrote: > >> + However, the binding does not attempt to define the specific method for >> + assigning chip select numbers. Since SPI chip select configuration is >> + flexible and non-standardized, it is left out of this binding with the >> + assumption that board specific platform code will be used to manage >> + chip selects. Individual drivers can define additional properties to >> + support describing the chip select layout. > > Yes, this looks like a problem to me. This means, SPI devices will need > two bindings - OF and platform?... Maybe define an spi_chipselect > OF-binding? Actually, spi devices have *neither*. :-) They bind to the SPI bus. Not the platform bus or of_platform bus. But that is Linux internal details; this discussion is about device tree bindings. Note that I did say that drivers can define additional properties for supporting chip select changes as needed. I'm just not attempting to encode them into the formal binding. There is simply just too many different ways to manipulate chip select signals and so I don't feel confident trying to define a *common* binding at this moment in time. At some point in the future when we have a number of examples to choose from then we can extend this binding with chip select related properties. As for the Linux internals, the 5200 SPI bus driver that I posted exports a function that allows another driver to call in and manipulated the CS lines before the transfer. It isn't the prettiest solution, but I'm not locked into the approach and that gives some time to consider cleaner interfaces. Cheers, g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd.