Re: [PATCH] ACPI: EC: Avoid _REG disconnect on GPIO IRQ defer

[Rafael J. Wysocki (Intel)]

On Wed, Jul 15, 2026 at 3:26 AM Zhu Ling <zhuling2709@xxxxxxxxxxxxxx> wrote:
>
> EC event delivery uses either a GPE or, on ACPI reduced hardware
> platforms, a GpioInt resource.  The GPE path does not have a provider
> lookup that can defer, but acpi_dev_gpio_irq_get() can return
> -EPROBE_DEFER for the GpioInt path.
>
> ec_install_handlers() currently installs the EC address space handler and
> executes _REG before looking up the GPIO IRQ.  If the GPIO lookup then
> defers, acpi_ec_setup() tears the handlers down again.  Removing the EC
> address space handler causes ACPICA to execute _REG for disconnect, so
> firmware may observe an EC OpRegion connected -> disconnected transition
> during one failed probe attempt.
>
> This is observable when the namespace EC reuses a boot EC that has already
> installed the EC address space handler.  A deferred namespace EC probe can
> disconnect the already usable boot EC OpRegion until a later reprobe
> connects it again.  AML that gates EC field accesses on _REG state can
> then return fallback values to other drivers during that window.
>
> Prepare the GPIOInt IRQ before publishing EC OpRegion availability to AML.
> This leaves the GPE path unchanged, keeps non-deferred GPIO lookup errors
> non-fatal as before, and still lets the existing acpi_ec_setup() error
> path clean up real handler installation failures.
>
> Fixes: f6484cadbcaf ("ACPI: EC: clean up handlers on probe failure in acpi_ec_setup()")
> Signed-off-by: Zhu Ling <zhuling2709@xxxxxxxxxxxxxx>
> ---
>  drivers/acpi/ec.c | 39 +++++++++++++++++++++++++--------------
>  1 file changed, 25 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
> index 64ad4cfa6208..26550879f43c 100644
> --- a/drivers/acpi/ec.c
> +++ b/drivers/acpi/ec.c
> @@ -1510,6 +1510,23 @@ static bool install_gpio_irq_event_handler(struct acpi_ec *ec)
>                                     IRQF_SHARED | IRQF_ONESHOT, "ACPI EC", ec) >= 0;
>  }
>
> +static int ec_prepare_gpio_irq(struct acpi_ec *ec, struct acpi_device *device)
> +{
> +       int irq;
> +
> +       if (!device || ec->gpe >= 0 || ec->irq >= 0)
> +               return 0;
> +
> +       /* ACPI reduced hardware platforms use a GpioInt from _CRS. */
> +       irq = acpi_dev_gpio_irq_get(device, 0);
> +       if (irq == -EPROBE_DEFER)
> +               return irq;
> +       if (irq >= 0)
> +               ec->irq = irq;
> +
> +       return 0;
> +}
> +
>  /**
>   * ec_install_handlers - Install service callbacks and register query methods.
>   * @ec: Target EC.
> @@ -1524,7 +1541,6 @@ static bool install_gpio_irq_event_handler(struct acpi_ec *ec)
>   * Return:
>   * -ENODEV if the address space handler cannot be installed, which means
>   *  "unable to handle transactions",
> - * -EPROBE_DEFER if GPIO IRQ acquisition needs to be deferred,
>   * or 0 (success) otherwise.
>   */
>  static int ec_install_handlers(struct acpi_ec *ec, struct acpi_device *device,
> @@ -1557,19 +1573,6 @@ static int ec_install_handlers(struct acpi_ec *ec, struct acpi_device *device,
>         if (!device)
>                 return 0;
>
> -       if (ec->gpe < 0) {
> -               /* ACPI reduced hardware platforms use a GpioInt from _CRS. */
> -               int irq = acpi_dev_gpio_irq_get(device, 0);
> -               /*
> -                * Bail out right away for deferred probing or complete the
> -                * initialization regardless of any other errors.
> -                */
> -               if (irq == -EPROBE_DEFER)
> -                       return -EPROBE_DEFER;
> -               else if (irq >= 0)
> -                       ec->irq = irq;
> -       }
> -
>         if (!test_bit(EC_FLAGS_QUERY_METHODS_INSTALLED, &ec->flags)) {
>                 /* Find and register all query methods */
>                 acpi_walk_namespace(ACPI_TYPE_METHOD, ec->handle, 1,
> @@ -1647,6 +1650,14 @@ static int acpi_ec_setup(struct acpi_ec *ec, struct acpi_device *device, bool ca
>  {
>         int ret;
>
> +       /*
> +        * GPIO IRQ lookup can defer.  Do it before publishing the EC
> +        * OpRegion to AML to avoid a spurious _REG(disconnect).
> +        */
> +       ret = ec_prepare_gpio_irq(ec, device);
> +       if (ret)
> +               return ret;
> +
>         /* First EC capable of handling transactions */
>         if (!first_ec)
>                 first_ec = ec;

Applied as 7.3 material, thanks!