Re: [PATCH] pinctrl: baytrail: show output gpio state correctly on Intel Baytrail

[Mika Westerberg]

On Mon, Nov 03, 2014 at 05:27:43PM +0200, Mika Westerberg wrote:
> On Mon, Nov 03, 2014 at 09:00:48AM -0600, Felipe Balbi wrote:
> > On Mon, Nov 03, 2014 at 11:24:02AM +0200, Mika Westerberg wrote:
> > > On Fri, Oct 31, 2014 at 11:45:09AM -0700, David Cohen wrote:
> > > > > I think adding the module exit + allowing this driver to be a module
> > > > > would be a good approach. Then we don't need to force generic x86 kernel
> > > > > binaries to always have this driver. Unless Mathias or Mika knows a
> > > > > constraint to force this driver to be builtin only.
> > > > 
> > > > It helps if I CC them when asking for feedback :)
> > > > 
> > > > Mathias, Mika, do you know any constraint that forces pinctrl-baytrail
> > > > to be bool?
> > > 
> > > The only constraint that has been keeping this driver as bool is that
> > > some machines like, Asus T100, uses ACPI GPIO operation regions for
> > > toggling GPIOs to get things like sensor hub powered on. The GPIO
> > > operation region code does not yet handle -EPROBE_DEFER so only way to
> > > ensure that the operation region is there is to have the driver compiled
> > > in to the kernel.
> > 
> > But that's not enough excuse to have every single x86 in the market
> > shipping with this driver. Think about a distro kernel, most likely this
> > gets enabled and it's wrong in 80% of the cases.
> 
> True, but see below.
> 
> > It would be nicer to add EPROBE_DEFER support, convert this into
> > tristate and have default = M if BAYTRAIL, or something.
> 
> If it were simple as that we would have done that already. Please check
> drivers/gpio/gpiolib-acpi.c:acpi_gpio_adr_space_handler() and tell me
> how we can do that.

Actually the above is not the problem because we already have registered
the GPIO chip and hence we have the GPIO available to the firmware code.

The real problem is that if the ACPI GPIO operation handler is not there
at the time firmware decides to do something it will just skip things
that depend on the operation region. So if it has a GPIO that is used to
turn on sensor hub or touch panel or whatever, this will not be done and
it results that the device in question might not work properly.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/