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

[Felipe Balbi]

Hi,

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.
> 
> The problem is that it is *firmware* code that decides to use the GPIO
> at some random point in time and we have no way to tell it to retry
> later when the GPIO is available.

which means that even with the driver built-in, there is still the
possibility that firmware will try to access it before
pinctrl-baytrail's init function is called and you'd end up in the same
situation.

The fact is that currently you're forcing every x86 (even non-Intel) to
ship with this driver statically linked into it just because a small
percent of x86 systems might need to have this ready-to-go early enough.

Unfortunately I don't know ACPI enough to tell you if there is a way to
tell firmware "hey, you can use GPIOs now", so I'l refrain from
commenting on that. But that doesn't change the fact that this is wrong.

-- 
balbi

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