Re: [RFC][PATCH] ACPI: EC: Make evaluate acpi_ec_add() _REG for EC operation regions

[Rafael J. Wysocki]

On Thu, Aug 4, 2022 at 3:57 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
>
> Hi,
>
> On 8/4/22 15:51, Rafael J. Wysocki wrote:
> > Hi Hans,
> >
> > On Thu, Aug 4, 2022 at 1:57 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> >>
> >> Hi Rafael,
> >>
> >> Sorry for the slow response...
> >
> > No sweat.
> >
> >> On 7/7/22 21:31, Rafael J. Wysocki wrote:
> >>> On Wed, Jul 6, 2022 at 10:26 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> >>>>
> >>>> Hi,
> >>>>
> >>>> On 7/6/22 14:37, Rafael J. Wysocki wrote:
> >>>>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >>>>>
> >>>>> acpi_ec_ecdt_probe() is called between acpi_load_tables() and
> >>>>> acpi_enable_subsystem().  It passes ACPI_ROOT_OBJECT as ec->handle
> >>>>> to acpi_ec_setup() and so ACPI_ROOT_OBJECT is passed to
> >>>>> acpi_install_address_space_handler() via ec_install_handlers().
> >>>>>
> >>>>> Next, acpi_ns_validate_handle() converts it to acpi_gbl_root_node
> >>>>> which is passed to acpi_ev_install_space_handler() and the handler is
> >>>>> installed for acpi_gbl_root_node.
> >>>>>
> >>>>> Now, acpi_gbl_root_node is passed to acpi_ev_execute_reg_methods() which
> >>>>> evaluates _REG for any ACPI_ADR_SPACE_EC regions it can find in the
> >>>>> namespace which should not be necessary, because the OS is expected to
> >>>>> make the ECDT operation regions available before evaluating any AML, so
> >>>>> in particular AML is not expected to check the evaluation of _REG before
> >>>>> it accesses these operation regions (see ACPI 6.4, Section 6.5.4,
> >>>>> exception 2 [1]).  Doing that is also problematic, because the _REG
> >>>>> methods for the ACPI_ADR_SPACE_EC regions may depend on various _INI, so
> >>>>> they should be be evaluated before running acpi_initialize_objects() [2].
> >>>>>
> >>>>> Address this problem by modifying acpi_install_address_space_handler()
> >>>>> to avoid evaluating _REG for ACPI_ADR_SPACE_EC regions when the handler
> >>>>> is installed for acpi_gbl_root_node which indicates the ECDT case.
> >>>>>
> >>>>> However, this needs to be accompanied by an EC driver change to
> >>>>> actually trigger the evaluation of _REG for the ACPI_ADR_SPACE_EC
> >>>>> regions when it finds the EC object in the namespace.
> >>>>>
> >>>>> Link: https://uefi.org/specs/ACPI/6.4/06_Device_Configuration/Device_Configuration.html#reg-region # [1]
> >>>>> Link: https://github.com/acpica/acpica/pull/786 # [2]
> >>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >>>>> ---
> >>>>>
> >>>>> Note: This change doesn't make any practical difference on any of the systems
> >>>>> in my office.
> >>>>>
> >>>>> ---
> >>>>>  drivers/acpi/acpica/evxfregn.c |   12 ++++++++++++
> >>>>>  drivers/acpi/ec.c              |    7 +++++++
> >>>>>  2 files changed, 19 insertions(+)
> >>>>>
> >>>>> Index: linux-pm/drivers/acpi/ec.c
> >>>>> ===================================================================
> >>>>> --- linux-pm.orig/drivers/acpi/ec.c
> >>>>> +++ linux-pm/drivers/acpi/ec.c
> >>>>> @@ -1632,6 +1632,13 @@ static int acpi_ec_add(struct acpi_devic
> >>>>>                       acpi_handle_debug(ec->handle, "duplicated.\n");
> >>>>>                       acpi_ec_free(ec);
> >>>>>                       ec = boot_ec;
> >>>>> +                     /*
> >>>>> +                      * Uninstall the EC address space handler and let
> >>>>> +                      * acpi_ec_setup() install it again along with
> >>>>> +                      * evaluating _REG methogs associated with
> >>>>> +                      * ACPI_ADR_SPACE_EC operation regions.
> >>>>> +                      */
> >>>>> +                     ec_remove_handlers(ec);
> >>>>
> >>>> This will call the _REG method to get called with ACPI_REG_DISCONNECT (0)
> >>>> as second argument which may lead to unexpected consequences so I'm not
> >>>> in favor of doing things this way.
> >>>>
> >>>> IMHO it would be much better to instead have flags; or if flags are
> >>>> disliked a separate function to only call _REG later on.
> >>>
> >>> I'm aware of the _REG(EC, 0) part, but I thought that it might be the
> >>> right thing to do.
> >>>
> >>> First off, I'm a bit concerned about leaving the EC address space
> >>> handler attached to the root node after we have discovered the proper
> >>> EC object in the namespace, because that's inconsistent with the "no
> >>> ECDT" case.
> >>
> >> True, but in the ECDT case the EC opregion should work anywhere
> >> according to the spec, so I believe it is consistent with the spec.
> >
> > That's until the proper EC object is discovered, though.
> >
> >>> It leaves a potential problem on the table too, because acpi_ec_add()
> >>> changes boot_ec->handle from ACPI_ROOT_OBJECT to ec->handle and if
> >>> ec_remove_handlers() is called for it after that, it will fail to
> >>> remove the handler, but it will clear the
> >>> EC_FLAGS_EC_HANDLER_INSTALLED flag (so the change above is actually
> >>> incorrect, because it should remove the handler before changing
> >>> boot_ec->handle).
> >>
> >> You are right, but this can be fixed by keeping track of the handle
> >> used when registering the handler, e.g. something like this:
> >>
> >> From fceb436703bc8f0e29b7613246a83c039b631cb4 Mon Sep 17 00:00:00 2001
> >> From: Hans de Goede <hdegoede@xxxxxxxxxx>
> >> Date: Thu, 4 Aug 2022 13:38:35 +0200
> >> Subject: [PATCH] ACPI: EC: Fix EC address space handler unregistration
> >>
> >> When an ECDT table is present the EC address space handler gets registered
> >> on the root node. So to unregister it properly the unregister call also
> >> must be done on the root node.
> >>
> >> Store the ACPI handle used for the acpi_install_address_space_handler()
> >> call and use te same handle for the acpi_remove_address_space_handler()
> >> call.
> >>
> >> Reported-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> >> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> >> ---
> >>  drivers/acpi/ec.c       | 4 +++-
> >>  drivers/acpi/internal.h | 1 +
> >>  2 files changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
> >> index 1e93677e4b82..6aa8210501d3 100644
> >> --- a/drivers/acpi/ec.c
> >> +++ b/drivers/acpi/ec.c
> >> @@ -1483,6 +1483,7 @@ 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_handle = ec->handle;
> >>         }
> >>
> >>         if (call_reg && !test_bit(EC_FLAGS_EC_REG_CALLED, &ec->flags)) {
> >> @@ -1543,7 +1544,8 @@ static int ec_install_handlers(struct acpi_ec *ec, struct acpi_device *device,
> >>  static void ec_remove_handlers(struct acpi_ec *ec)
> >>  {
> >>         if (test_bit(EC_FLAGS_EC_HANDLER_INSTALLED, &ec->flags)) {
> >> -               if (ACPI_FAILURE(acpi_remove_address_space_handler(ec->handle,
> >> +               if (ACPI_FAILURE(acpi_remove_address_space_handler(
> >> +                                       ec->address_space_handler_handle,
> >>                                         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);
> >> diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
> >> index 628bf8f18130..140af11d0c39 100644
> >> --- a/drivers/acpi/internal.h
> >> +++ b/drivers/acpi/internal.h
> >> @@ -173,6 +173,7 @@ enum acpi_ec_event_state {
> >>
> >>  struct acpi_ec {
> >>         acpi_handle handle;
> >> +       acpi_handle address_space_handler_handle;
> >>         int gpe;
> >>         int irq;
> >>         unsigned long command_addr;
> >> --
> >
> > This works.
> >
> > I would rename address_space_handler_handle to something like
> > address_space_handler_holder.
>
> Ok, I'll rename this for the official upstream submission.
>
> >> This fixes ec_remove_handlers() without requiring (IMHO) risky changes
> >> where we call _REG() multiple times.
> >>
> >> Also note that ec_remove_handlers() is only ever called from
> >> acpi_ec_driver.remove which in practice never runs since the EC never
> >> gets hot unplugged (arguably the entire remove code could be removed).
> >
> > Indeed.
> >
> >>> But in order to move the EC address space handler under the EC object,
> >>> it needs to be uninstalled and for this purpose AML needs to be told
> >>> that it's not there, so evaluating _REG(EC, 0) seems reasonable to me
> >>> even though I agree that it is somewhat risky.
> >>
> >> I'm pretty worried that calling _REG(EC, 0) will cause problems
> >> the _REG handlers run pretty early on and various BIOS/ACPI table
> >> authors seem to (ab)use this to do some sort of early setup
> >> of some things in _REG, That is pretty much how this whole thread
> >> has started. Given all the weirdness some ACPI tables do in their
> >> _REG handling running _REG 3 times:
> >>
> >> 1. _REG(EC, 1)
> >> 2. _REG(EC, 0)
> >> 3. _REG(EC, 1)
> >>
> >> really seems like a bad idea to me. I have the feeling that this is
> >> asking for trouble.
> >
> > OK, fair enough.
> >
> >>> Second, the spec is kind of suggesting doing it (cf. the "These
> >>> operation regions may become inaccessible after OSPM runs
> >>> _REG(EmbeddedControl, 0)" comment in the _REG definition section).
> >>
> >> That is boilerplate documentation copy and pasted from all the
> >> other address space handlers the spec defines. I'm not sure if
> >> Windows ever actually calls _REG(EmbeddedControl, 0) and I would
> >> not be surprised if Windows does not do this.
> >>
> >>> Moreover, I don't quite like the ACPI_NO_INSTALL_SPACE_HANDLER flag,
> >>> because it causes the "handler installation" to actually do something
> >>> else.
> >>
> >> As mentioned before (IIRC) I would be more then happy to respin both
> >> the ACPICA as well as the Linux ACPI bits to introduce / use 2 new
> >> functions for this, lets say:
> >>
> >> 1. acpi_install_address_space_handler_no__reg()
> >
> > So we need this in ACPICA, because it doesn't make sense to drop and
> > re-acquire the namespace mutex around _REG evaluation in the non-EC
> > case.
>
> Right, just like the flags changes in this RFC getting this fixed
> will require some work on the ACPICA side + then Linux changes
> using the new ACPICA functions.
>
> > But as stated before I would prefer to introduce an
> > acpi_install_address_space_handler_internal() taking an additional
> > BOOL run__reg argument  and I would define
> > acpi_install_address_space_handler() and the new
> > acpi_install_address_space_handler_no__reg() as wrappers around it.
>
> Right, that is how it will look like inside ACPICA, but API consumers
> will just see a new acpi_install_address_space_handler_no__reg()
> getting introduced.

Well, one more thing about it.

This would be a very generic interface with a very specific use case.
Moreover, the use case in question is already detectable in
acpi_install_address_space_handler().

Namely, the _REG evaluation can be skipped automatically if an
ACPI_ADR_SPACE_EC handler is installed at the root of the ACPI
namespace (because it doesn't even make sense to evaluate _REG then).
If this is done, we don't need the extra argument.

Hmm?

> >
> >> 2. acpi_run_address_space_handler__reg()
> >
> > So this would just be a wrapper around acpi_ev_execute_reg_methods()
> > that would acquire the namespace mutex around it, right?  [I think
> > that it should also acquire acpi_gbl_namespace_rw_lock along the lines
> > of acpi_walk_namespace(), though.]
>
> Ack.
>
> > I would call it acpi_execute_reg_methods() then.
>
> acpi_execute_reg_methods() works for me.
>
> I'll try to prepare a new ACPICA pull-req with the discussed
> changes + a Linux series on top sometime the coming few weeks.
>
> Regards,
>
> Hans
>