On 01/04/2012 04:00 PM, Grant Likely wrote: > On Wed, Jan 4, 2012 at 1:00 PM, Stephen Warren <swarren@xxxxxxxxxx> wrote: >> Rob Herring wrote at Wednesday, January 04, 2012 12:54 PM: >>> On 01/04/2012 12:39 PM, Stephen Warren wrote: >>>> Tegra20's GPIO controller has 7 banks, and Tegra30's controller has 8 >>>> banks. Allow the number of banks to be configured at run-time by the >>>> device tree. >> ... >>>> diff --git a/Documentation/devicetree/bindings/gpio/gpio_nvidia.txt >> ... >>>> Required properties: >>>> - compatible : "nvidia,tegra20-gpio" >>>> - reg : Physical base address and length of the controller's registers. >>>> +- nvidia,num-banks : The number of GPIO banks. This should be 7 for >>>> + Tegra20 and 8 for Tegra30. This must match the number of interrupt >>>> + specifiers in the interrupts property. >>> >>> You can determine the number of banks based on the compatible property >>> rather than needing an additional property. >> >> That's certainly possible. >> >> However, if say nvidia,tegraNNN-gpio has 9 banks, we then have to >> explicitly edit the driver to know that, whereas by using a property, >> we wouldn't have to change the driver at all to support a future GPIO >> controller. So, isn't it better to explicitly represent this in DT? >> >> Note that I have no idea how many GPIO banks our future chips will have, >> so this might not turn out to save any work at all, but perhaps. > > It's an engineering/design decision that requires taste and instinct. > Either approach is fine, you decide which one will be the best in the > long term. Agreed. I'm really fine with it either way. Trying to predict future h/w is a bit pointless IMO. H/w designers always find new ways to do things differently. i.MX family has gpio interrupts hooked up 3 different ways for example. How would you handle the case that the banks are sparsely implemented? Is adding support for a different number of banks every couple of years really an issue? It's much more important to have properties for which change with every board. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
