[PATCH] gpio: exynos4: Add device tree support

[Grant Likely]

On Wed, Oct 12, 2011 at 09:45:25PM +0530, Thomas Abraham wrote:
> On 12 October 2011 20:41, Rob Herring <robherring2 at gmail.com> wrote:
> > On 10/11/2011 11:06 AM, Thomas Abraham wrote:
> >> On 11 October 2011 21:00, Rob Herring <robherring2 at gmail.com> wrote:
> >>> On 10/11/2011 10:19 AM, Thomas Abraham wrote:
> >>>> Hi Rob,
> >>>>
> >>>> On 11 October 2011 20:41, Rob Herring <robherring2 at gmail.com> wrote:
> >>>>> Thomas,
> >>>>>
> >>>>> On 10/11/2011 03:16 AM, Thomas Abraham wrote:
> >>>>>> As gpio chips get registered, a device tree node which represents the
> >>>>>> gpio chip is searched and attached to it. A translate function is also
> >>>>>> provided to convert the gpio specifier into actual platform settings
> >>>>>> for pin function selection, pull up/down and driver strength settings.
> >>>>>>
> >>>>>> Signed-off-by: Thomas Abraham <thomas.abraham at linaro.org>
> >>>>>> ---
> >>>>>> This patch is based on the latest consolidated Samsung GPIO driver available
> >>>>>> in the following tree:
> >>>>>>   https://github.com/kgene/linux-samsung.git  branch: for-next
> >>>>>>
> >>>>>>  .../devicetree/bindings/gpio/gpio-samsung.txt      |   30 +++++++++++
> >>>>>>  drivers/gpio/gpio-samsung.c                        |   53 ++++++++++++++++++++
> >>>>>>  2 files changed, 83 insertions(+), 0 deletions(-)
> >>>>>>  create mode 100644 Documentation/devicetree/bindings/gpio/gpio-samsung.txt
> >>>>>>
> >>>>>> diff --git a/Documentation/devicetree/bindings/gpio/gpio-samsung.txt b/Documentation/devicetree/bindings/gpio/gpio-samsung.txt
> >>>>>> new file mode 100644
> >>>>>> index 0000000..883faeb
> >>>>>> --- /dev/null
> >>>>>> +++ b/Documentation/devicetree/bindings/gpio/gpio-samsung.txt
> >>>>>> @@ -0,0 +1,30 @@
> >>>>>> +Samsung Exynos4 GPIO Controller
> >>>>>> +
> >>>>>> +Required properties:
> >>>>>> +- compatible: Format of compatible property value should be
> >>>>>> +  "samsung,exynos4-gpio-<controller_name>". Example: For GPA0 controller, the
> >>>>>> +  compatible property value should be "samsung,exynos4-gpio-gpa0".
> >>>>>
> >>>>> Isn't gpa0 an instance of the h/w, not a version?
> >>>>
> >>>> GPA0 is a instance of the gpio controller. There are several such
> >>>> instances and there could be differences in those instances such as
> >>>> the number of GPIO lines managed by that gpio controller instance.
> >>>>
> >>>
> >>> That doesn't seem like a reason to have different compatible strings.
> >>> Does that affect the programming model of the controller? Unused lines
> >>> whether at the board level or SOC level shouldn't really matter.
> >>
> >>
> >> No, that does not affect the programming of the controller. The reason
> >> for the instance name extension in compatible string is to match the
> >> gpio_chip with a gpio controller node. When matched, the of_node
> >> pointer of the gpio_chip is set to point to that controller node.
> >>
> >> This might not be the best possible implementation but the device tree
> >> support code in this patch is dictated by the structure of the
> >> existing gpio driver code. As you suggested previously, I will look at
> >> reworking the gpio driver a little later but for now, there was a need
> >> for working gpio dt solution to make progress on dt support for other
> >> controllers.
> >
> > Linux should provide clues about what's needed in a binding, but the
> > binding should not be defined based on current Linux code. Doing the
> > binding one way and changing it later is not a good plan.
> 
> Ok. When starting on this, two compatible values where used for the
> gpio controllers, one was "samsung,exynos4-gpio" and another was
> "samsung,exynos4-gpio-<ctrl_name>". And when the gpio dt support would
> mature, the second compatible value could be dropped. Non-linux
> platforms could always use the generic "samsung,exynos4-gpio"
> compatible value to match. I moved to using only
> "samsung,exynos4-gpio-<ctrl_name>" just before sending this patch
> because I was not sure of the right approach.
> 
> >
> > I think you need to convert all users of gpio over as well so you can
> > move to dynamic gpio_chip creation and gpio numbering. Or maybe you can
> > match based on base address? This is going to be a common problem as
> > gpio is converted over to DT. Perhaps Grant or others have suggestions
> > on the approach to use.
> 
> Yes, I agree with you about the dynamic gpio_chip creation and gpio
> numbering. Probably, I should have focussed more on this before moving
> to dt support for other controllers.
> 
> But matching based on base address is still an option if that is
> better than matching with compatible values as defined currently. The
> 'struct samsung_gpio_chip' which encapsulates 'struct gpio_chip' has
> information about the base address of the gpio controller. The match
> of gpio device node with 'struct gpio_chip' can be quickly moved over
> to base address matching. Would this be better than the current
> approach?

That's what I would do.

g.