Hi,
On 02-02-17 11:41, Mika Westerberg wrote:
On Wed, Feb 01, 2017 at 09:42:57AM -0800, Dmitry Torokhov wrote:
On Mon, Jan 23, 2017 at 11:05:14AM +0100, Hans de Goede wrote:
Hi,
On 22-01-17 23:20, Dmitry Torokhov wrote:
On Sun, Jan 22, 2017 at 09:00:08PM +0100, Hans de Goede wrote:
On some x86 tablets we cannot directly access the GPIOs as they are
claimed by the ACPI tables, so check it the i2c client is not being
power-managed by ACPI before trying to get the power pin GPIO.
Why do we even get this GPIO if driver is not supposed to be using it?
I'd much rather gpio provider hid it from the driver instead of every
driver having this check.
The problem is that the gpio subsys does not really know about ACPI
managed GPIOs the way this works is that the firmware sets a special
"reserved for firmware use" bit in the gpio control register and
directly bit-bangs the gpio control register when it wants to toggle
the gpio. So there is no awareness of these gpios being reserved
(as gpios) at the ACPI level AFAICT.
The hardware specific low-level gpio chip driver checks this bit
when we request the gpio and returns -EBUSY.
I'd say that, if GPIOs are reserved for firmware use, and kernel should
not or can not touch them, then they should not be visible, if not to
the gpio core, then to consumers for sure.
Let's add Mika and Linus.
It is not always possible for the GPIO driver to find out if a certain
GPIO is reserved for the firmware use or not. I don't think we have any
API in gpiolib that allows excluding certain GPIOs though.
What we do for example with the ACPI OpRegion GPIOs is that gpiolib
reserves those automatically thus preventing any consumer from using
those.
Right, but that would result in a -EBUSY error from gpiod_get, so
iow gpiod_get_optional would still fail and not just return NULL as it
would if the requested gpio does not exist?
IOW even if that was happening here, we would still need to handle
either -EBUSY and treat it as gpiod_get_optional returning NULL, or
we need the acpi_bus_power_manageable check the patch from this
thread is adding, right ?
Regards,
Hans
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