On Fri, Nov 20, 2015 at 08:27:35PM +0200, Vladimir Zapolskiy wrote:
> On 20.11.2015 16:13, Rob Herring wrote:
> > On Fri, Nov 20, 2015 at 03:29:52AM +0200, Vladimir Zapolskiy wrote:
> >> For the purpose of better description of NXP LPC32xx GPIO controller
> >> hardware in device tree format, extend the existing description with
> >> device tree subnodes, which represent 6 GPIO banks within the
> >> controller.
> >>
> >> Note, client interface to the GPIO controller is untouched.
> >>
> >> Signed-off-by: Vladimir Zapolskiy <vz@xxxxxxxxx>
> >> ---
> >> .../devicetree/bindings/gpio/gpio_lpc32xx.txt | 121 ++++++++++++++++++++-
> >> 1 file changed, 120 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/gpio/gpio_lpc32xx.txt b/Documentation/devicetree/bindings/gpio/gpio_lpc32xx.txt
> >> index 4981936..d2da63c 100644
> >> --- a/Documentation/devicetree/bindings/gpio/gpio_lpc32xx.txt
> >> +++ b/Documentation/devicetree/bindings/gpio/gpio_lpc32xx.txt
> >> @@ -15,7 +15,43 @@ Required properties:
> >> 2) pin number
> >> 3) optional parameters:
> >> - bit 0 specifies polarity (0 for normal, 1 for inverted)
> >> -- reg: Index of the GPIO group
> >> +- #address-cells: should be 2, which stands for GPIO bank id and
> >> + physical base address of this GPIO bank.
> >
> > Now you need special code to do address translation. I'd really think
> > twice about doing this.
>
> Correct, address translation code is needed here...
>
> > Why do you need the bank number?
>
> Only one reason -- backward compatibility in sense of referencing a GPIO
> line on client's side. This API design is broken, I agree.
What client exactly? Between the dtb and kernel or kernel and userspace
or ...?
> Honestly I would prefer to get rid of this "feature", new code allows to
> reference on client's side either a parent GPIO controller device node,
> or bank nodes, probably the improvement can be done in a few steps?
>
> - this change,
> - convert clients to reference a GPIO bank directly,
> - remove root GPIO controller (e.g. make it "simple-bus") and convert
> GPIO banks to "gpio-controller"s.
>
> Can an evolution like this happen?
You generally don't want bindings to evolve.
> >> + gpio_p2: gpio-controller@2 {
> >> + reg = <2 0x10 0x18>;
> >> + gpio-bank-name = "p2";
> >> + gpios = <13>;
> >> + gpio-no-output-state;
> >> + };
> >> +
> >> + gpio_gpio: gpio-controller@3 {
> >> + reg = <3 0x00 0x1C>;
> >
> > This overlaps with bank 2.
>
> Yes, it is. Thousand thanks to hardware designers.
Then you might want to split these into 2 regions. The problem is
request_resource does not work with overlapping resources. Or just don't
do subnodes. If there is not a lot of variations in the subnode data,
then just leave that information in the kernel.
Rob
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