linux-kernel - Re: [PATCH v4 0/6] ACPI / EC: Fix GPE handling related races.

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Message-ID: <8695025.SuvMBZB7tJ@vostro.rjw.lan>
Date:	Thu, 05 Feb 2015 16:19:48 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Lv Zheng <lv.zheng@...el.com>
Cc:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 0/6] ACPI / EC: Fix GPE handling related races.

On Thursday, February 05, 2015 04:24:29 PM Lv Zheng wrote:
> This patchset is based on ACPICA 20150204 release.
> 
> This patchset introduces a GPE raw handler mode and switches EC driver into
> a GPE raw handler mode user.
> 
> The EC driver is a kind of the hardware driver that wants to control the
> interrupt handling itself (for example, implementing the storming
> prevention or the burst mode). But it has no mean to do so using the EC
> firmware provided commands. The EC driver has to rely on the GPE APIs to
> achieve the interrupt controlling.
> Due to the shortcoming of the current ACPICA GPE APIs, the EC driver is
> using the GPE APIs in a racy way. We then can see many issues between the
> ACPICA internal GPE controlling and the EC driver's GPE handling. Such
> races prevents us from correctly root causing other EC issues. This
> patchset fixes the GPE related race issues by holding the EC state machine
> lock for the whole EC GPE handling process:
>   Lock(EC)        <- EC lock
>   if (STS==1)     <- GPE API
>     STS=0         <- GPE API
>   EC_SC read      <- EC GPE handler
>   EC_SC handled   <- EC GPE handler
>   Unlock(EC)      <- EC lock
> 
> We can see several GPE handling stuffs improved by applying this patchset
> because of EC/GPE races fixed:
> 1. Some platforms may suffer from GPE loss, which is because GPE is handled
>    in the polling mode with its GPE indication left uncleared, the
>    uncleared indication may stop further GPEs from being triggered.
>    This patchset can make sure the indication has been cleared before
>    handling, thus it may have fixed the potential root cause of the bugs
>    that were originally fixed by the MSI quirk.
> 2. We originally can see many no-op EC GPE handler invocations, which is
>    becaue GPE can be handled in the task context after the GPE IRQ handler
>    is invoked, then when the driver goes back to the handler, there is no
>    indication left for it to handle.
>    This patchset can reduce the number of no-op EC GPE handler invocations
>    to almost 0 by fixing the races, thus it may have fixed the potential
>    root cause of the issues that were originally fixed by the storming
>    condition threshold quirk.
> 
> Lv Zheng (6):
>   ACPICA: Events: Introduce ACPI_GPE_DISPATCH_RAW_HANDLER to fix 2
>     issues for the current GPE APIs.
>   ACPICA: Events: Introduce acpi_set_gpe()/acpi_finish_gpe() to reduce
>     divergences.
>   ACPICA: Events: Enable APIs to allow interrupt/polling adaptive
>     request based GPE handling model.
>   ACPI / EC: Fix several GPE handling issues by deploying
>     ACPI_GPE_DISPATCH_RAW_HANDLER mode.
>   ACPI / EC: Reduce ec_poll() by referencing the last register access
>     timestamp.
>   ACPI / EC: Update revision due to raw handler mode.
> 
>  drivers/acpi/acpica/evgpe.c     |   52 +++++++++++++++---
>  drivers/acpi/acpica/evgpeblk.c  |    2 +
>  drivers/acpi/acpica/evgpeinit.c |    6 +-
>  drivers/acpi/acpica/evgpeutil.c |    6 +-
>  drivers/acpi/acpica/evxface.c   |  115 +++++++++++++++++++++++++++++++++++----
>  drivers/acpi/acpica/evxfgpe.c   |  114 ++++++++++++++++++++++++++++++++++++++
>  drivers/acpi/ec.c               |  104 ++++++++++++++++++++++++++++++-----
>  include/acpi/acpixf.h           |    8 +++
>  include/acpi/actypes.h          |   11 ++--
>  9 files changed, 375 insertions(+), 43 deletions(-)

Whole series queued up for 3.20, thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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