Re: [PATCH] ACPICA: make acpi_load_table() return table index

[Ferry Toth]

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.

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"));