linux-kernel - Re: [PATCH v2 RESEND 05/18] x86, ACPICA: Split acpi_boot_table

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Date:	Mon, 05 Aug 2013 15:26:37 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	robert.moore@...el.com, lv.zheng@...el.com, lenb@...nel.org,
	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	akpm@...ux-foundation.org, tj@...nel.org, trenn@...e.de,
	yinghai@...nel.org, jiang.liu@...wei.com, wency@...fujitsu.com,
	laijs@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	izumi.taku@...fujitsu.com, mgorman@...e.de, minchan@...nel.org,
	mina86@...a86.com, gong.chen@...ux.intel.com,
	vasilis.liaskovitis@...fitbricks.com, lwoodman@...hat.com,
	riel@...hat.com, jweiner@...hat.com, prarit@...hat.com,
	zhangyanfei@...fujitsu.com, yanghy@...fujitsu.com, x86@...nel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 RESEND 05/18] x86, ACPICA: Split acpi_boot_table_init() into two parts.

On Monday, August 05, 2013 11:21:51 AM Tang Chen wrote:
> Hi Rafael,
> 
> On 08/02/2013 09:00 PM, Rafael J. Wysocki wrote:
> ......
> >> This patch splits acpi_boot_table_init() into two steps:
> >> 1. Parse RSDT, which cannot be overrided, and initialize
> >>     acpi_gbl_root_table_list. (step 1 + 2 above)
> >> 2. Install all ACPI tables into acpi_gbl_root_table_list.
> >>     (step 3 + 4 above)
> >>
> >> In later patches, we will do step 1 + 2 earlier.
> >
> > Please note that Linux is not the only user of the code you're modifying, so
> > you need to make it possible to use the existing functions.
> >
> > In particular, acpi_tb_parse_root_table() can't be modified the way you did it,
> > because that would require all of the users of ACPICA to be modified.
> 
> OK, I understand it. Then how about acpi_tb_install_table() ?
> 
> acpi_tb_install_table() is also an ACPICA API. But can we split the
> acpi_initrd_table_override part out ? Like the following:

I'm not sure what you mean.  acpi_tb_install_table() doesn't call
acpi_initrd_table_override() directly.

Do you want to split the acpi_tb_table_override() call out of it?

I'm afraid that still wouldn't be OK.

> 1. Initialize acpi_gbl_root_table_list earlier, and install all tables
>     provided by firmware.
> 2. Find SRAT in initrd. If no overridden SRAT, get the SRAT in 
> acpi_gbl_root_table_list
>     directly. And mark hotpluggable memory. (This the job I want to do.)
> 3. DO acpi_initrd_table_override job.
> 
> Finally it will work like the current kernel. The only difference is:
> Before the patch-set, it try to do override first, and then install 
> firmware tables.
> After the patch-set, it installs firmware tables, and then do the override.

I think I understand what you're trying to achieve and I don't have objections
agaist the goal, but the matter is *how* to do that.

Why don't you do something like this:
(1) Introduce two new functions that will each do part of
    acpi_tb_parse_root_table() such that calling them in sequence, one right
    after the other, will be exactly equivalent to the current
    acpi_tb_parse_root_table().
(2) Redefine acpi_tb_parse_root_table() as a wrapper calling those two new
    function one right after the other.
(3) Make Linux use the two new functions directly instead of calling
    acpi_tb_parse_root_table()?

Then, Linux will use your new functions and won't call acpi_tb_parse_root_table()
at all, but the other existing users of ACPICA may still call it without any
modifications.

Does this make sense to you?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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