linux-kernel - Re: [PATCH v2 02/18] ARM64 / ACPI: Get RSDP and ACPI boot-time tables

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Message-ID: <53F31D14.70006@arm.com>
Date:	Tue, 19 Aug 2014 10:47:00 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <Mark.Rutland@....com>
CC:	Sudeep Holla <sudeep.holla@....com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Al Stone <al.stone@...aro.org>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>
Subject: Re: [PATCH v2 02/18] ARM64 / ACPI: Get RSDP and ACPI boot-time tables



On 19/08/14 10:35, Hanjun Guo wrote:
> On 2014-8-19 2:30, Sudeep Holla wrote:
>> On 04/08/14 16:28, Hanjun Guo wrote:
>>> From: Al Stone <al.stone@...aro.org>
>>>
>>> As we want to get ACPI tables to parse and then use the information
>>> for system initialization, we should get the RSDP (Root System
>>> Description Pointer) first, it then locates Extended Root Description
>>> Table (XSDT) which contains all the 64-bit physical address that
>>> pointer to other boot-time tables.
>>>
>>> Introduce acpi.c and its related head file in this patch to provide
>>> fundamental needs of extern variables and functions for ACPI core,
>>> and then get boot-time tables as needed.
>>>     - asm/cpu.h need for ACPI core and will be updated in the future to
>>>       add definitions for arch_(un)register_cpu which are required for
>>>       ACPI based physical CPU hotplug;
>>

[...]

>>> +/*
>>> + * acpi_boot_table_init() called from setup_arch(), always.
>>> + *    1. find RSDP and get its address, and then find XSDT
>>> + *    2. extract all tables and checksums them all
>>> + *
>>> + * We can parse ACPI boot-time tables such as FADT, MADT after
>>> + * this function is called.
>>> + */
>>> +void __init acpi_boot_table_init(void)
>>> +{
>>> +    /* If acpi_disabled, bail out */
>>> +    if (acpi_disabled)
>>> +        return;
>>> +
>>> +    /* Initialize the ACPI boot-time table parser. */
>>> +    if (acpi_table_init()) {
>>
>> Can't we call acpi_table_init directly in setup ?
>> IIUC x86 has acpi_boot_table_init as it parses Boot Flags
>> table(ACPI_SIG_BOOT)
>
> Yes, we can. But I think it not a big deal to dot that, if that
> makes the code more readable, I will update it.
>

I agree, but I actually wanted to check if we ever have to use/parse
Simple Boot Flag Table on ARM64 which is reserved but not part of ACPI
spec. I assume x86 use either for Legacy reason or firmware expects it.

Regards,
Sudeep

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