Re: Missing default handler for the EmbeddedControl OpRegion

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Wednesday, May 8, 2024 2:20:59 PM CEST Heikki Krogerus wrote:
> On Mon, May 06, 2024 at 07:45:07PM +0200, Rafael J. Wysocki wrote:
> > Hi,
> > 
> > On Mon, Apr 29, 2024 at 4:55 PM Heikki Krogerus
> > <heikki.krogerus@linux.intel.com> wrote:
> > >
> > > Hi,
> > >
> > > There's a bug that is caused by an EmbeddedControl OpRegion which is
> > > declared inside the scope of a specific USB Type-C device (PNP0CA0):
> > > https://bugzilla.kernel.org/show_bug.cgi?id=218789
> > 
> > And in this bug you are essentially proposing to install the EC
> > OpRegion handler at the namespace root instead of the EC device.
> > 
> > This sounds reasonable, although AFAICS this is a matter of modifying
> > the EC driver (before the EC OpRegion handler is installed by the EC
> > drvier, ACPICA has no way to handle EC address space accesses anyway).
> > 
> > > It looks like that's not the only case where that OpRegion ID is used
> > > outside of the EC device scope. There is at least one driver in Linux
> > > Kernel (drivers/platform/x86/wmi.c) that already has a custom handler
> > > for the EmbeddedControl OpRegion, and based on a quick search, the
> > > problem "Region EmbeddedControl (ID=3) has no handler" has happened
> > > with some other devices too.
> > 
> > AFAICS, installing the EC address space handler at the EC device
> > object itself is not based on any sound technical arguments, it's just
> > been always done this way in Linux.  It's quite possible that the EC
> > address space handler should have been installed at the namespace root
> > from the outset.
> 
> Okay, thank you for the explanation. So can we simply change it like
> this (I may have still misunderstood something)?

Roughly speaking, yes, but it is missing an analogous change around
the removal.

Please see the appended patch (which I have created independently in
the meantime).  It doesn't break stuff for me and Andy points out that
there are examples of EmbeddedControl OpRegions outside the EC device
scope in the spec (see Section 9.17.15 in ACPI 6.5, for instance).

So I think that this change can be made relatively safely (but adding Hans and
Mario to the CC in case they know something that might be broken by it).


> diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
> index 02255795b800..6b9dd27171ee 100644
> --- a/drivers/acpi/ec.c
> +++ b/drivers/acpi/ec.c
> @@ -1488,7 +1488,7 @@ static int ec_install_handlers(struct acpi_ec *ec, struct acpi_device *device,
>  
>         if (!test_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags)) {
>                 acpi_ec_enter_noirq(ec);
> -               status = acpi_install_address_space_handler_no_reg(ec->handle,
> +               status = acpi_install_address_space_handler_no_reg(ACPI_ROOT_OBJECT,
>                                                                    ACPI_ADR_SPACE_EC,
>                                                                    &acpi_ec_space_handler,
>                                                                    NULL, ec);
> @@ -1497,7 +1497,7 @@ static int ec_install_handlers(struct acpi_ec *ec, struct acpi_device *device,
>                         return -ENODEV;
>                 }
>                 set_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags);
> -               ec->address_space_handler_holder = ec->handle;
> +               ec->address_space_handler_holder = ACPI_ROOT_OBJECT;
>         }
>  
>         if (call_reg && !test_bit(EC_FLAGS_EC_REG_CALLED, &ec->flags)) {
> 

---
 drivers/acpi/ec.c       |   10 +++++-----
 drivers/acpi/internal.h |    1 -
 2 files changed, 5 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/ec.c
===================================================================
--- linux-pm.orig/drivers/acpi/ec.c
+++ linux-pm/drivers/acpi/ec.c
@@ -1488,7 +1488,7 @@ static int ec_install_handlers(struct ac
 
 	if (!test_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags)) {
 		acpi_ec_enter_noirq(ec);
-		status = acpi_install_address_space_handler_no_reg(ec->handle,
+		status = acpi_install_address_space_handler_no_reg(ACPI_ROOT_OBJECT,
 								   ACPI_ADR_SPACE_EC,
 								   &acpi_ec_space_handler,
 								   NULL, ec);
@@ -1497,11 +1497,10 @@ static int ec_install_handlers(struct ac
 			return -ENODEV;
 		}
 		set_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags);
-		ec->address_space_handler_holder = ec->handle;
 	}
 
 	if (call_reg && !test_bit(EC_FLAGS_EC_REG_CALLED, &ec->flags)) {
-		acpi_execute_reg_methods(ec->handle, ACPI_ADR_SPACE_EC);
+		acpi_execute_reg_methods(ACPI_ROOT_OBJECT, ACPI_ADR_SPACE_EC);
 		set_bit(EC_FLAGS_EC_REG_CALLED, &ec->flags);
 	}
 
@@ -1555,8 +1554,9 @@ static void ec_remove_handlers(struct ac
 {
 	if (test_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags)) {
 		if (ACPI_FAILURE(acpi_remove_address_space_handler(
-					ec->address_space_handler_holder,
-					ACPI_ADR_SPACE_EC, &acpi_ec_space_handler)))
+						ACPI_ROOT_OBJECT,
+						ACPI_ADR_SPACE_EC,
+						&acpi_ec_space_handler)))
 			pr_err("failed to remove space handler\n");
 		clear_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags);
 	}
Index: linux-pm/drivers/acpi/internal.h
===================================================================
--- linux-pm.orig/drivers/acpi/internal.h
+++ linux-pm/drivers/acpi/internal.h
@@ -186,7 +186,6 @@ enum acpi_ec_event_state {
 
 struct acpi_ec {
 	acpi_handle handle;
-	acpi_handle address_space_handler_holder;
 	int gpe;
 	int irq;
 	unsigned long command_addr;