Re: [PATCH 6/6] gpio: tegra: Parameterize the number of banks

On Wed, Jan 4, 2012 at 1:00 PM, Stephen Warren [off-list ref] wrote:

Rob Herring wrote at Wednesday, January 04, 2012 12:54 PM:

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On 01/04/2012 12:39 PM, Stephen Warren wrote:

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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.

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diff --git a/Documentation/devicetree/bindings/gpio/gpio_nvidia.txt

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 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.

g.