Re: [PATCH 1/3] gpio / ACPI: add ACPI support

[Mathias Nyman]

On 11/09/2012 04:18 PM, Grant Likely wrote:
> On Fri, Nov 9, 2012 at 2:11 PM, Mathias Nyman
> <mathias.nyman@xxxxxxxxxxxxxxx>  wrote:
> > On 11/08/2012 09:38 PM, Mika Westerberg wrote:
> > ...
> >
> > > > > +#include<linux/errno.h>
> > > > > +#include<linux/gpio.h>
> > > > > +#include<linux/module.h>
> > > > > +#include<linux/acpi_gpio.h>
> > > > > +#include<linux/acpi.h>
> > > > > +
> > > > > +static int acpi_gpiochip_find(struct gpio_chip *gc, void *data)
> > > > > +{
> > > > > +       acpi_handle handle = data;
> > > > > +       acpi_handle gc_handle;
> > > > > +
> > > > > +       if (!gc->dev)
> > > > > +               return false;
> > > > > +
> > > > > +       gc_handle = gc->dev->acpi_handle;
> > > > > +       if (!gc_handle)
> > > > > +               return false;
> > > >
> > > >
> > > > This test is redundant with the next one... unless 'handle' is also NULL
> > > > :-)
> > > >
> > > > Is it at all possible for multiple gpiochips to be used for a single
> > > > ACPI gpio controller node? Such as if the gpio controller has multiple
> > > > banks that should be controlled separately? If so then this won't be
> > > > sufficient. I've got the same issue with DT support where the find
> > > > function needs to also check if the pin is provided by that specific
> > > > gpiochip.
> > >
> > >
> > > AFAIK no but I'll let Mathias to answer that as he knows this better.
> >
> >
> > I'm interpreting it the same way as Mika, max one actual controller per ACPI
> > device node
> >
> > The path (called ResourceSource in ACPI5 specs) in GpioIO/GpioInt resources
> > is a "string which uniquely identifies the GPIO controller referred to by
> > this descriptor."  The pin number is zero based controller relative.
> >
> > The  ACPI device controller node includes all other resources needed by the
> > controller driver (ioport/mem base, range, interrupt, and Hardware ID used
> > to pair with a driver)
> >
> > Checked a board with two identical gpio controllers on it and it had two
> > separate ACPI device node entries. (with only different io address base and
> > interrupt resources)
>
> That's not really the situation that I'm thinking about. What I mean
> is for a gpio controller that is more convenient for Linux to support
> using multiple gpiochips (Linux internal detail), even though there it
> is described with a single ACPI node.

Ok, now I get it.

Yes, in case a driver uses several gpiochips internally for different 
banks of a controller then all would have the same acpi_handle.
acpi_get_gpio() would use the gpiobase of the first gpiochip that 
matches the handle, even if it's the wrong one.

I guess It's possible to write a driver like that.
The only acpi enumerated driver with the acpi_handle set (soon coming to 
upstream) is not done like that.

Do you think this is a case that should be solved now?  or just expect 
acpi gpio device driver to not use several gpiochips in one driver?

-Mathias
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