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To:     linux-kernel@vger.kernel.org
From:   Ferry Toth <fntoth@gmail.com>
Subject: Re: [PATCH] ACPICA: make acpi_load_table() return table index
Date:   Fri, 13 Sep 2019 18:48:28 +0200
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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@vosn.de]
>> Sent: Friday, September 13, 2019 12:44 AM
>> To: Moore, Robert <robert.moore@intel.com>
>> Cc: Shevchenko, Andriy <andriy.shevchenko@intel.com>; Schmauss, Erik <erik.schmauss@intel.com>; Rafael J. Wysocki <rjw@rjwysocki.net>; Len Brown <lenb@kernel.org>; Jacek Anaszewski <jacek.anaszewski@gmail.com>; Pavel Machek <pavel@ucw.cz>; Dan Murphy <dmurphy@ti.com>; linux-acpi@vger.kernel.org; devel@acpica.org; linux-kernel@vger.kernel.org; Ferry Toth <ftoth@telfort.nl>; nikolaus.voss@loewensteinmedical.de
>> 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@siemens.com>
> 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.

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"));
>