linux-kernel - Re: [PATCH 1/4] ACPI: Provide support for ACPI table adding via OS

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Date:	Tue, 18 Feb 2014 12:51:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Renninger <trenn@...e.de>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org, devel@...ica.org,
	mingo@...hat.com, ck@...rad-kostecki.de, tglx@...utronix.de,
	rjw@...ysocki.net
Subject: Re: [PATCH 1/4] ACPI: Provide support for ACPI table adding via OS

On 02/18/2014 10:44 AM, Thomas Renninger wrote:
> On Tuesday, February 18, 2014 10:27:23 AM H. Peter Anvin wrote:
>> Why can't you add SSDTs? It would be particularly useful.
> 
> There are 2 ways how ACPI tables get added:
>    - Via pointer from a root table (XSDT or RSDT iirc)
>    - Via load statement inside of ACPI context when ACPI BIOS
>      code gets executed (iirc the physical address is passed).
> 
> The latter is only for SSDTs.
> The problem is that you if you add an SSDT early, it might
> have been intended for overriding when an SSDT gets dynamically
> loaded later when the system is up which is particular useful as
> well if you want to debug this specific BIOS table.
> 
> This could be workarounded via a boot param:
> acpi=allow_ssdt_adding
> But this is not nice. Maybe someone has a more elegant idea.
> Something could still be added if someone is really needing this.

Since adding SSDTs is one of the things I really can imagine one would
do, I think we need to figure out how to do that.  I would think that
overriding would be the exception case.

	-hpa

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