linux-kernel - Re: [PATCH 13/21] x86, acpi: Try to find SRAT in firmware earlier.

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Date:	Wed, 24 Jul 2013 18:12:03 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	akpm@...ux-foundation.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 13/21] x86, acpi: Try to find SRAT in firmware earlier.

On 07/24/2013 04:49 AM, Tejun Heo wrote:
> On Fri, Jul 19, 2013 at 03:59:26PM +0800, Tang Chen wrote:
......
>> +	for (pos = 0;
>> +	     pos<  acpi_gbl_root_table_list.current_table_count;
>> +	     pos++) {
>> +		if (!ACPI_COMPARE_NAME
>> +		    (&(acpi_gbl_root_table_list.tables[pos].signature),
>> +		    signature))
>
> Hohumm... creative formatting.  Can't you just cache the tables
> pointer in a local variable with short name and avoid the creativity?

OK, followed.

>
>> +			continue;
>> +
>> +		memcpy(out_desc,&acpi_gbl_root_table_list.tables[pos],
>> +		       sizeof(struct acpi_table_desc));
>> +
>> +		return_ACPI_STATUS(AE_OK);
>> +	}
>> +
>> +	return_ACPI_STATUS(AE_NOT_FOUND);
>
> Also, if we already know that SRAT is what we want, I wonder whether
> it'd be simpler to store the location of SRAT somewhere instead of
> trying to be generic with the early processing.

Do you mean get the SRAT's address without touching any ACPI global
variables, such as acpi_gbl_root_table_list ?

The physical addresses of all tables is stored in RSDT (Root System
Description Table), which is the root table. We need to parse RSDT
to get SRAT address.

Using acpi_gbl_root_table_list is very convenient. The initialization
of acpi_gbl_root_table_list is using acpi_os_map_memory(), so it can be
done before init_mem_mapping() and relocate_initrd().

With acpi_gbl_root_table_list initialized, we can iterate it and find
SRAT easily. Otherwise, we have to do the same procedure to parse RSDT,
and find SRAT, which I don't think could be any simpler. I think reuse
the existing acpi_gbl_root_table_list code is better.

Thanks.
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