On Fri, Feb 26, 2016 at 5:00 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Friday 26 February 2016 16:34:59 Carlo Caione wrote: >> On Fri, Feb 19, 2016 at 1:54 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> >> <cut> >> >> > This still really sounds like a mixed bag to me, which should better get represented >> > as a syscon node, except that there are also some more structured areas in >> > CBUS. >> > >> > Having just the registers between METAL_REVISION and HW_REV in a syscon >> > is clearly wrong, as that would include the pinctrl area that already has >> > a driver, but would not include some other parts that want the syscon. >> > >> > Maybe the best way is to make it compatible with both syscon and >> > simple-bus and put the other nodes underneath. That is still rather >> > ugly, but at least it works and can be extended. >> >> More on this topic. >> >> On the meson platforms (at least on the meson8 / meson8b) we have two >> buses: cbus and aobus. Since in cbus we have a bunch of scattered >> registers, Arnd suggested to make it compatible with both syscon and >> simple-bus. So my idea was actually to update the meson8b DTSI file >> adding the two buses to make it closer to the actual hardware. >> >> In the most simple cases moving the devices under the correct bus is a >> trivial operation since (of course) the same driver can be used when >> the device is attached to a different bus, like in the uart_AO case >> (http://lxr.free-electrons.com/source/arch/arm/boot/dts/meson8b.dtsi#L114). >> >> Unfortunately pinctrl is a different beast since it requires >> (http://lxr.free-electrons.com/source/drivers/pinctrl/meson/pinctrl-meson.c#L659) >> at least two subnodes: one accessing registers from aobus, and the >> other one from cbus. >> >> I know this is quite a peculiar case but I'm wondering what is the >> best way to approach this issue. >> >> 1) We could move only the pinctrl device outside both aobus and cbus >> but IMO this is ugly (at this point is probably better not having the >> two buses at all described in the DTS). >> 2) The second option is just to fix the driver so that the two >> subnodes are not strictly required. The problem with this second >> solution is that in the driver we still need to access some data >> (http://lxr.free-electrons.com/source/drivers/pinctrl/meson/pinctrl-meson8b.c#L873) >> that is specific to each bus. So we will end up having two different >> compatibles for the two buses (meson8b-pinctrl-aobus using data from >> 'ao-bank', and meson8b-pinctrl-cbus using data from 'banks'). >> 3) Another option is just to have the driver with a unique compatible >> poking the parent node (or just to another property) to determine on >> which bus it is so that it can use the correct bus-specific data. >> >> Any idea / feedback? > > Would it be possible to split the pin controller driver into two drivers > that each only access registers on one of the buses? Is that a split > that makes sense from the point of view of that driver? AFAICT (I'm not the driver author) there is no a really strict reason to have one single driver accessing registers on both buses. Of course the driver has to be changed a bit. Are you suggesting to have two different drivers with two different compatibles? -- Carlo Caione -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
