From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Sinan Kaya <okaya@codeaurora.org>
Cc: Wolfram Sang <wsa@the-dreams.de>,
Eric Auger <eric.auger@redhat.com>,
eric.auger.pro@gmail.com, linux-i2c@vger.kernel.org,
linux-kernel@vger.kernel.org,
"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Lan Tianyu <tianyu.lan@intel.com>
Subject: Re: [PATCH v2] i2c: Allow ACPI_I2C_OPREGION if I2C is built as a module
Date: Wed, 24 Jan 2018 16:24:48 +0200 [thread overview]
Message-ID: <20180124142448.GS27654@lahna.fi.intel.com> (raw)
In-Reply-To: <f498c1ef-0e15-3956-8e70-bca53ec2cac4@codeaurora.org>
On Wed, Jan 24, 2018 at 08:29:44AM -0500, Sinan Kaya wrote:
> +linux-acpi
>
> On 1/24/2018 1:27 AM, Mika Westerberg wrote:
> > On Wed, Jan 24, 2018 at 06:56:16AM +0100, Wolfram Sang wrote:
> >> On Wed, Jan 03, 2018 at 03:02:31PM +0100, Eric Auger wrote:
> >>> If I2C is built as a module, ACPI_I2C_OPREGION cannot be set
> >>> and any ACPI opregion calls targeting I2C fail with no opregion found.
> >>>
> >>> This patch allows ACPI_I2C_OPREGION to be enabled both if I2C is
> >>> built into the kernel or built as a module.
> >>>
> >>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> >>
> >> I recall that we had some discussion until ending up with the current
> >> solution. And I finally found it again:
> >>
> >> http://www.serverphorums.com/read.php?12,1001402
> >>
> >> In any case, I surely want Mika's ack on any change to ACPI related
> >> Kconfig symbols. Adding him to CC...
> >
> > So the problem is/was that what happens if you are in a middle of BIOS
> > AML code touching the opregion and someone unloads the opregion handler?
> > If you can quarantee nothing bad happens, then I'm fine with the patch :)
> >
>
> Rafael to correct me if I got this right.
>
> The behavior of the operating system is well defined in the ACPI specification.
>
> Here is what I tested recently:
>
> ACPI defines _REG method to inform firmware of presence/removal of an operating
> region.
>
> When driver gets loaded, ACPI calls the _REG method with 1 argument. When driver
> gets unloaded, ACPI call the _REG method with 0 argument.
>
> Firmware can use this notification to its advantage to determine when an I2C
> related functionality should be accessed or not.
>
> If firmware doesn't use the _REG method, ACPI defines that AML statements
> accessing the operating region are ignored.
>
> You'll also see a warning from ACPICA saying the OperatingRegion 9 is no longer
> accessible and AML code execution failed.
>
> Also note that someone can always unbind an I2C driver from ACPI even with built-in
> module.
Yes, that's right.
However, the I2C core parts are not removed when you unbind a driver and
the imporant piece is i2c_acpi_space_handler() which then stays in the
memory even if any of the drivers get removed. After this patch you can
also remove the i2c_acpi_space_handler() which might cause issues if
there is AML code running at the same time using the opregion.
Commit da3c6647ee08 ("I2C/ACPI: Clean up I2C ACPI code and Add
CONFIG_I2C_ACPI config") says following:
Current there is a race between removing I2C ACPI operation region
and ACPI AML code accessing. So make i2c core built-in if
CONFIG_I2C_ACPI is set.
But I don't remember all the details unfortunately so adding Rafael and
Tianyu if they can shed some more light into this ;-)
next prev parent reply other threads:[~2018-01-24 14:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-03 14:02 [PATCH v2] i2c: Allow ACPI_I2C_OPREGION if I2C is built as a module Eric Auger
2018-01-08 16:22 ` Sinan Kaya
2018-01-24 5:56 ` Wolfram Sang
2018-01-24 6:27 ` Mika Westerberg
2018-01-24 13:29 ` Sinan Kaya
2018-01-24 14:24 ` Mika Westerberg [this message]
2018-01-24 14:44 ` Andy Shevchenko
2018-01-24 14:59 ` Hans de Goede
2018-01-24 15:12 ` Sinan Kaya
2018-01-24 15:23 ` Hans de Goede
2018-01-24 15:37 ` Sinan Kaya
2018-01-24 16:09 ` Hans de Goede
2018-01-24 16:10 ` Sinan Kaya
2018-01-24 16:56 ` Auger Eric
2018-01-24 14:46 ` Andy Shevchenko
2018-01-24 14:49 ` Sinan Kaya
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180124142448.GS27654@lahna.fi.intel.com \
--to=mika.westerberg@linux.intel.com \
--cc=eric.auger.pro@gmail.com \
--cc=eric.auger@redhat.com \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-i2c@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=okaya@codeaurora.org \
--cc=rafael.j.wysocki@intel.com \
--cc=tianyu.lan@intel.com \
--cc=wsa@the-dreams.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).