Re: ACPI: Do not call _STA on battery devices with unmet dependencies

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Hi,

On 01/23/2018 01:24 AM, Schmauss, Erik wrote:
Hi,
-----Original Message-----
From: Hans de Goede [mailto:hdegoede@xxxxxxxxxx]
Sent: Saturday, January 20, 2018 4:48 AM
To: Schmauss, Erik <erik.schmauss@xxxxxxxxx>
Cc: Rafael J . Wysocki <rjw@xxxxxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>;
Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; Moore, Robert
<robert.moore@xxxxxxxxx>; Zheng, Lv <lv.zheng@xxxxxxxxx>; linux-
acpi@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx
Subject: Re: ACPI: Do not call _STA on battery devices with unmet dependencies

Hi,

On 19-01-18 22:03, Schmauss, Erik wrote:

-----Original Message-----
From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-
owner@xxxxxxxxxxxxxxx] On Behalf Of Bjorn Helgaas
Sent: Thursday, January 18, 2018 11:11 AM
To: Hans de Goede <hdegoede@xxxxxxxxxx>
Cc: Rafael J . Wysocki <rjw@xxxxxxxxxxxxx>; Len Brown
<lenb@xxxxxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; Moore, Robert
<robert.moore@xxxxxxxxx>; Zheng, Lv <lv.zheng@xxxxxxxxx>; linux-
acpi@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx
Subject: Re: ACPI: Do not call _STA on battery devices with unmet
dependencies

On Thu, Jan 18, 2018 at 05:03:55PM +0100, Hans de Goede wrote:

Hi Hans,

Hi All,

The ACPI code already contains quite a bit of code to not bind theFrom the acpi_get_object_info() documentation in drivers/acpi/acpica/nsxfname.c:

 * Note: This interface is intended to be used during the initial device
 * discovery namespace traversal. Therefore, no complex methods can be
 * executed, especially those that access operation regions.

ACPI-battery until all deps for an ACPI battery device have been
met, but on some devices calling _STA before all deps are met is a
problem too because the _STA method uses an i2c OpRegion there.

Could you explain why _STA method using an I2C OpRegion is problematic?

It is problematic if we call the _STA method before the handler for the OpRegion
has been installed, this series delays / avoids calling _STA before the OpRegion
has been installed.

Thanks for the explanation.
I'm looking at the ACPI spec and from what it said about _STA, I gathered that _STA is allowed to have side-effects to named objects within the AML namespace. So removing _STA from acpi_get_object_info seems a little dangerous... Is there a reason why you cannot remove or delay the call to acpi_get_object_info instead? Chapter 6 section 1 of the ACPI spec also states that it's possible for _HID and _ADR to read from operation regions as well. Is it common convention that these _HID and _ADR objects do not access operation regions?

From the acpi_get_object_info() documentation in drivers/acpi/acpica/nsxfname.c:

 * Note: This interface is intended to be used during the initial device
 * discovery namespace traversal. Therefore, no complex methods can be
 * executed, especially those that access operation regions.

So if _STA can have side-effects then that seems like another reason to NOT
call it from acpi_get_object_info().

If something depends on the side-effects (which I doubt) then the code which
depends on it should really call _STA explicitly itself.

Regards,

Hans



Here is the DSDT of the device I'm seeing this on:
https://fedorapeople.org/~jwrdegoede/toshiba-click-mini-dsdt.dsl

This looks like interesting info, but (a) this link isn't mentioned
in the actual patches, and (b) it's conceivable that fedorapeople.org could go
away someday.
If this were a PCI series, I would suggest opening a report at
bugzilla.kernel.org, attaching the DSL there, and including the link in the
patch changelog.

This series modifies the kernel to not call _STA until all deps are
met, mirroring the binding behavior of the battery driver.

Without this series a total of 32 ACPI errors get printend to the
console on boot, there are 4 errors per _STA call, 2 battery devices
on this system and 4 _STA calls per battery device.

The first commit is a preparation commit for making the ACPICA
changes in the 4th commit, this commit is necessary to not break
things after the ACPICA changes.

The second commit modifies acpi_bus_get_status to not call _STA on
battery devices until all deps are met. This fixes 2 of the 4 too
early _STA calls triggering these errors.

The third commit makes the device instantiation code use
acpi_bus_get_status instead of acpi_bus_get_status_handle so that
the code to get the initial status also does not makes 1 too early _STA call.

The fourth commit changes the ACPICA acpi_get_object_info function
to not call _STA. Only 1 user (which is fixed in the first commit)
cares about acpi_device_info.current_status. And the ACPICA code has
this
comment:

   * Note: This interface is intended to be used during the initial
device
   * discovery namespace traversal. Therefore, no complex methods can be
   * executed, especially those that access operation regions.
Therefore, do
   * not add any additional methods that could cause problems in this area.
   * Because of this reason support for the following methods has
been
removed:
   * this was the fate of the _SUB method which was found to cause such
   * problems and was removed (11/2015).

The described problems with the _SUB method clearly also apply to
the _STA method, so removing it from acpi_get_object_info seems like
it is the right thing to do here. This too fixes 1 too early _STA
call, so that with all
4 patches in place we've fixed all 4 too early _STA calls.

Regards,

Hans
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