commit c103a10f690cc49054c52f493eeeff143d5f59e7
author Mika Westerberg <mika.westerberg@linux.intel.com> Fri Oct 30 12:02:05 2015 +0200
committer Linus Walleij <linus.walleij@linaro.org> Sat Oct 31 22:12:31 2015 +0100
tree c60e2d045841421a361aa0c2c0787069a173a60b
parent bc6a73bbfba5d8325b0e659545ce2f3ad983829b

gpio / ACPI: Allow shared GPIO event to be read via operation region

In Microsoft Surface3 the GPIO detecting lid state is shared between GPIO
event and operation region. Below is simplied version of the DSDT from
Surface3 including relevant parts:

    Scope (GPO0)
    {
        Name (_AEI, ResourceTemplate ()
        {
            GpioInt (Edge, ActiveBoth, Shared, PullNone, 0x0000,
                "\\_SB.GPO0", 0x00, ResourceConsumer, ,
                )
                {   // Pin list
                    0x004C
                }
        })

        OperationRegion (GPOR, GeneralPurposeIo, Zero, One)
        Field (GPOR, ByteAcc, NoLock, Preserve)
        {
            Connection (
                GpioIo (Shared, PullNone, 0x0000, 0x0000,
                    IoRestrictionNone, "\\_SB.GPO0", 0x00,
                    ResourceConsumer,,)
                    {   // Pin list
                        0x004C
                    }
            ),
            HELD,   1
        }

        Method (_E4C, 0, Serialized)  // _Exx: Edge-Triggered GPE
        {
            If ((HELD == One))
            {
                ^^LID.LIDB = One
            }
            Else
            {
                ^^LID.LIDB = Zero
                Notify (LID, 0x80) // Status Change
            }

            Notify (^^PCI0.SPI1.NTRG, One) // Device Check
        }
    }

When GPIO 0x4c changes we call ASL method _E4C which tries to read HELD
field (the same GPIO). This triggers following error on the console:

    ACPI Error: Method parse/execution failed [\_SB.GPO0._E4C]
        (Node ffff88013f4b4438), AE_ERROR (20150930/psparse-542)

The error happens because ACPI GPIO operation region handler
(acpi_gpio_adr_space_handler()) tries to acquire the very same GPIO which
returns an error (-EBUSY) because the GPIO is already reserved for the GPIO
event.

Fix this so that we "borrow" the event GPIO if we find the GPIO belongs to
an event. Allow this only for GPIOs that are read.

To be able to go through acpi_gpio->events list for operation region access
we need to make sure the list is properly initialized whenever GPIO chip is
registered.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=106571
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>