From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Fri, 15 Jun 2012 11:32:33 +0100 Subject: [PATCH 09/14] i2c: Add Device Tree support to the Nomadik I2C driver In-Reply-To: <4FDA341C.8010501@linaro.org> References: <1339428307-3850-1-git-send-email-lee.jones@linaro.org> <1339428307-3850-10-git-send-email-lee.jones@linaro.org> <4FD6F0E8.5040606@linaro.org> <4FD83AAD.2010701@linaro.org> <4FD88761.9050703@linaro.org> <20120614183636.GB30185@sirena.org.uk> <4FDA341C.8010501@linaro.org> Message-ID: <20120615103233.GA19046@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jun 14, 2012 at 07:57:32PM +0100, Lee Jones wrote: > On 14/06/12 19:36, Mark Brown wrote: >> On Wed, Jun 13, 2012 at 01:28:17PM +0100, Lee Jones wrote: >> >>> Device Tree. However, we have just as much control by keeping them >>> in separate structs in the C file and selecting the right one using >>> the compatible sting. >> >> You're not understanding Linus' point. The compatible string isn't >> useful here because properties like the maximum clock rate of the bus >> depend on the board design, not the silicon. The controller may be >> perfectly happy to run at a given rate but other devices on the bus or >> the electrical engineering of the PCB itself may restrict this further. > > And you're not understanding mine. ;) > > You can have multiple compatible strings for a single driver. Which one > you reference from the Device Tree will dictate which group of settings > are used, including variation of clock rates. However, if you list these settings separately, rather than selecting them based on a compatible string, it means when other board designs come along, you don't have to modify the kernel code to provide yet another compatible to settings translation in the code - you can keep all that information entirely within DT with no kernel code mods. I thought that was partly the point of DT...