RE: [PATCH] ACPICA: make acpi_load_table() return table index
From: Nikolaus Voss
Date: Mon Sep 23 2019 - 05:05:22 EST
On Thu, 19 Sep 2019, Moore, Robert wrote:
-----Original Message-----
From: Nikolaus Voss [mailto:nv@xxxxxxx]
Sent: Wednesday, September 18, 2019 7:32 AM
To: Moore, Robert <robert.moore@xxxxxxxxx>
Cc: Ferry Toth <fntoth@xxxxxxxxx>; Shevchenko, Andriy <andriy.shevchenko@xxxxxxxxx>; Schmauss, Erik <erik.schmauss@xxxxxxxxx>; Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx>; Pavel Machek <pavel@xxxxxx>; Dan Murphy <dmurphy@xxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Subject: RE: [PATCH] ACPICA: make acpi_load_table() return table index
On Wed, 18 Sep 2019, Moore, Robert wrote:
-----Original Message-----
From: Nikolaus Voss [mailto:nv@xxxxxxx]
Sent: Monday, September 16, 2019 2:47 AM
To: Moore, Robert <robert.moore@xxxxxxxxx>
Cc: Ferry Toth <fntoth@xxxxxxxxx>; Shevchenko, Andriy
<andriy.shevchenko@xxxxxxxxx>; Schmauss, Erik
<erik.schmauss@xxxxxxxxx>; Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; Len
Brown <lenb@xxxxxxxxxx>; Jacek Anaszewski
<jacek.anaszewski@xxxxxxxxx>; Pavel Machek <pavel@xxxxxx>; Dan Murphy
<dmurphy@xxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Subject: RE: [PATCH] ACPICA: make acpi_load_table() return table index
On Fri, 13 Sep 2019, Moore, Robert wrote:
-----Original Message-----
From: Ferry Toth [mailto:fntoth@xxxxxxxxx]
Sent: Friday, September 13, 2019 9:48 AM
To: Shevchenko, Andriy <andriy.shevchenko@xxxxxxxxx>; Moore, Robert
<robert.moore@xxxxxxxxx>
Cc: Nikolaus Voss <nv@xxxxxxx>; Schmauss, Erik
<erik.schmauss@xxxxxxxxx>; Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; Len
Brown <lenb@xxxxxxxxxx>; Jacek Anaszewski
<jacek.anaszewski@xxxxxxxxx>; Pavel Machek <pavel@xxxxxx>; Dan Murphy
<dmurphy@xxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; nikolaus.voss@xxxxxxxxxxxxxxxxxxxxx;
Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Subject: Re: [PATCH] ACPICA: make acpi_load_table() return table
index
Hello all,
Sorry to have sent our message with cancelled e-mail address. I have correct this now.
Op 13-09-19 om 17:12 schreef Shevchenko, Andriy:
On Fri, Sep 13, 2019 at 05:20:21PM +0300, Moore, Robert wrote:
-----Original Message-----
From: Nikolaus Voss [mailto:nv@xxxxxxx]
Sent: Friday, September 13, 2019 12:44 AM
To: Moore, Robert <robert.moore@xxxxxxxxx>
Cc: Shevchenko, Andriy <andriy.shevchenko@xxxxxxxxx>; Schmauss,
Erik <erik.schmauss@xxxxxxxxx>; Rafael J. Wysocki
<rjw@xxxxxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Jacek Anaszewski
<jacek.anaszewski@xxxxxxxxx>; Pavel Machek <pavel@xxxxxx>; Dan
Murphy <dmurphy@xxxxxx>; linux-acpi@xxxxxxxxxxxxxxx;
devel@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Ferry Toth
<ftoth@xxxxxxxxxx>; nikolaus.voss@xxxxxxxxxxxxxxxxxxxxx
Subject: RE: [PATCH] ACPICA: make acpi_load_table() return table
index
Bob,
On Thu, 12 Sep 2019, Moore, Robert wrote:
The ability to unload an ACPI table (especially AML tables such as
SSDTs) is in the process of being deprecated in ACPICA -- since it
is also deprecated in the current ACPI specification. This is
being done because of the difficulty of deleting the namespace
entries for the table. FYI, Windows does not properly support this function either.
ok, I see it can be a problem to unload an AML table with all it's
consequences e.g. with respect to driver unregistering in setups
with complex dependencies. It will only work properly under certain
conditions
- nevertheless acpi_tb_unload_table() is still exported in ACPICA and we should get this working as it worked before.
AcpiTbUnloadTable is not exported, it is an internal interface only
-- as recognized by the "AcpiTb".
In Linux it became a part of ABI when the
commit 772bf1e2878ecfca0d1f332071c83e021dd9cf01
Author: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Date: Fri Jun 9 20:36:31 2017 +0200
ACPI: configfs: Unload SSDT on configfs entry removal
appeared in the kernel.
And the commit message explains quite well why it is an important feature:
"This allows to change SSDTs without rebooting the system.
It also allows to destroy devices again that a dynamically loaded SSDT created.
The biggest problem AFAIK is that under linux, many drivers cannot be unloaded. Also, there are many race conditions as the namespace entries "owned" by an SSDT being unloaded are deleted (out from underneath a driver).
This is widely similar to the DT overlay behavior."
I'm not sure that I want to change the interface to AcpiLoadTable
just for something that is being deprecated. Already, we throw an
ACPI_EXCEPTION if the Unload operator is encountered in the AML
byte stream. The same thing with AcpiUnloadParentTable - it is being deprecated.
ACPI_EXCEPTION ((AE_INFO, AE_NOT_IMPLEMENTED,
"AML Unload operator is not supported"));
Bob, what is your suggestion to fix the regression then?
We could revert acpi_configfs.c to use
acpi_tb_install_and_load_table() instead of acpi_load_table(), leaving
loaded APCI objects uninitalized, but at least, unloading will work again.
I guess my next question is: why do you want to unload a table in the
first place?
Because it worked before and there are people who rely on it. If it's
deprecated there should be a user notification and a reasonable
end-of-life timeline to give these users a chance to develop an
alternative solution.
So, I still don't understand why this no longer works. We did not make
any purposeful changes in this area - AFAIK. Bob
It's because the acpi_configfs driver formerly used
acpi_tb_install_and_load_table() which returns the table index, but
doesn't resolve the references. It now uses acpi_load_table() which
resolves the references, but doesn't return the table index, so unloading
doesn't work any more.
Niko
Do we have any other options?
Niko