On 01/13/2012 02:55 PM, Stephen Warren wrote: > Rob Herring wrote at Thursday, January 05, 2012 10:25 AM: >> 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. > > Thinking about this some more, I'm tempted to rework this patch to remove > the extra DT property and just "detect" the number of banks based on the > length of the interrupts property, (well, actually the number of IRQ > resources that the platform device has) since each bank has its own > interrupt. Does anyone disagree with doing that? Sounds fine too me. 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
