Message-ID: <CAJZ5v0h=bYE_2iF+RgWsXvyq9euYM71pVWuE7gKX18fU0nAx0Q@mail.gmail.com>
Date:   Thu, 4 Aug 2022 17:19:27 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] ACPI: EC: Make evaluate acpi_ec_add() _REG for EC
 operation regions

On Thu, Aug 4, 2022 at 5:11 PM Hans de Goede <hdegoede@...hat.com> wrote:
>
> Hi,
>
> On 8/4/22 16:11, Rafael J. Wysocki wrote:
> > On Thu, Aug 4, 2022 at 4:08 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> >>
> >> On Thu, Aug 4, 2022 at 3:57 PM Hans de Goede <hdegoede@...hat.com> 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@...hat.com> 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@...hat.com> wrote:
> >>>>>>>
> >>>>>>> Hi,
> >>>>>>>
> >>>>>>> On 7/6/22 14:37, Rafael J. Wysocki wrote:
> >>>>>>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >>>>>>>>
> >>>>>>>> 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@...el.com>
> >>>>>>>> ---
> >>>>>>>>
> >>>>>>>> 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@...hat.com>
> >>>>> 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@...nel.org>
> >>>>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> >>>>> ---
> >>>>>  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.
> >
> > More specifically, bail out of acpi_ev_execute_reg_methods() early if
> > the space ID is ACPI_ADR_SPACE_EC and node is the namespace root, in
> > which case the EC address space can be regarded as a "must always be
> > accessible" one.
>
> I'm not really in favor of hiding the conditions under which _REG
> calling is skipped in this way.
>
> If you look at this RFC patch int introduces a EC_FLAGS_EC_REG_CALLED
> flag in drivers/acpi/ec.c and then later on uses that flag to
> determine that _REG still needs to be called when ec_install_handlers()
> is called the second time when actually probing/parsing the ACPI EC
> object.
>
> If we hide the conditions under which _REG is skipped inside
> ACPICA, then determining  when to call the new
> acpi_execute_reg_methods() method is going to be somewhat tricky and
> more over anyone reading the code then needs to also figure out that
> acpica originally skipped this and under which conditions it was
> orignally skipped.
>
> IMHO having drivers/acpi/ec.c in full control over when to skip
> (and thus also when to run _REG later) is cleaner then splitting
> this over 2 different code bases.

OK

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