Message-ID: <52E2986B.802@linaro.org>
Date:	Fri, 24 Jan 2014 17:44:27 +0100
From:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Hanjun Guo <hanjun.guo@...aro.org>
CC:	Matthew Garrett <mjg59@...f.ucam.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Olof Johansson <olof@...om.net>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Linaro-acpi] [PATCH 04/20] ARM64 / ACPI: Introduce arm_core.c
 and its related head file

Hi Lorenzo,

W dniu 24.01.2014 13:53, Lorenzo Pieralisi pisze:
> Hi Hanjun,
>
> On Fri, Jan 24, 2014 at 09:09:40AM +0000, Hanjun Guo wrote:
>> On 2014?01?23? 23:56, Tomasz Nowicki wrote:
>>> Hi Lorenzo,
>>>
>>> W dniu 22.01.2014 12:54, Lorenzo Pieralisi pisze:
>>>> On Fri, Jan 17, 2014 at 12:24:58PM +0000, Hanjun Guo wrote:
>>>>
>>>> [...]
>>>>
>>>>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>>>>> index bd9bbd0..2210353 100644
>>>>> --- a/arch/arm64/kernel/setup.c
>>>>> +++ b/arch/arm64/kernel/setup.c
>>>>> @@ -41,6 +41,7 @@
>>>>> #include <linux/memblock.h>
>>>>> #include <linux/of_fdt.h>
>>>>> #include <linux/of_platform.h>
>>>>> +#include <linux/acpi.h>
>>>>>
>>>>> #include <asm/cputype.h>
>>>>> #include <asm/elf.h>
>>>>> @@ -225,6 +226,11 @@ void __init setup_arch(char **cmdline_p)
>>>>>
>>>>> arm64_memblock_init();
>>>>>
>>>>> + /* Parse the ACPI tables for possible boot-time configuration */
>>>>> + acpi_boot_table_init();
>>>>> + early_acpi_boot_init();
>>>>> + acpi_boot_init();
>>>>> +
>>>>> paging_init();
>>>>
>>>> Can I ask you please why we need to parse ACPI tables before
>>>> paging_init() ?
>>> This is for future usage and because of couple of reasons. Mainly SRAT
>>> table parsing should be done (before paging_init()) for proper NUMA
>>> initialization and then paging_init().
>
> Thank you for the explanation. I still have some questions:
>
> 1) What are the other reasons ?
If we agreed that we need SRAT parsing before paging_init() the second 
reason is all implications related to that. I mean if we want to make 
ACPI tables parseable before paging_init(), we need early_ioremap 
mechanism and __acpi_map_table() fixes. In that case, IMHO, it is better 
to please it in the right place now. early_ioremap is object of UEFI 
support patch set.
> 2) NUMA is not supported at the moment and I reckon SRAT needs updating
>     since the only way to associate a CPU to a memory node is through
>     a local APIC id that is non-existent on ARM and at least deserves a
>     new entry.
Right, that requires further work on SRAT.
>
> I am still not sure that providing a hook for parsing the ACPI tables before
> paging_init() is the main focus at the moment, it is probably best, as we've
> mentioned manifold times, to make sure that the infrastructure to detect
> ACPI vs DT at run-time is in place in the kernel and allows us to boot
> either with ACPI or DT, in a mutual exclusive way (same binary kernel
> supporting both, runtime detection/decision on what data to use, ACPI tables
> vs DT nodes, detection made once for all and NOT on a per property basis).
>
> I will have a look at SRAT and how it is used on x86, and get back to you on
> this.
>
> [...]
>
>>>>> + * acpi_boot_table_init() and acpi_boot_init()
>>>>> + * called from setup_arch(), always.
>>>>> + * 1. checksums all tables
>>>>> + * 2. enumerates lapics
>>>>> + * 3. enumerates io-apics
>>>>> + *
>>>>> + * acpi_table_init() is separated to allow reading SRAT without
>>>>> + * other side effects.
>>>>> + */
>>>>> +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()) {
>>>>> + disable_acpi();
>>>>> + return;
>>>>> + }
>>>>> +}
>>>>> +
>>>>> +int __init early_acpi_boot_init(void)
>>>>> +{
>>>>> + /*
>>>>> + * If acpi_disabled, bail out
>>>>> + */
>>>>> + if (acpi_disabled)
>>>>> + return -ENODEV;
>>>>> +
>>>>> + /*
>>>>> + * Process the Multiple APIC Description Table (MADT), if present
>>>>> + */
>>>>> + early_acpi_process_madt();
>>>>> +
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +int __init acpi_boot_init(void)
>>>>> +{
>>>>> + /*
>>>>> + * If acpi_disabled, bail out
>>>>> + */
>>>>> + if (acpi_disabled)
>>>>> + return -ENODEV;
>>>>> +
>>>>> + acpi_table_parse(ACPI_SIG_FADT, acpi_parse_fadt);
>>>>> +
>>>>> + /*
>>>>> + * Process the Multiple APIC Description Table (MADT), if present
>>>>> + */
>>>>> + acpi_process_madt();
>>>>> +
>>>>> + return 0;
>>>>> +}
>>>>
>>>> Well, apart from having three init calls, one returning void and two
>>>> returning proper values, do not understand why, and do not understand
>>>> why we need three calls in the first place...why should we process MADT
>>>> twice in two separate calls ? What is supposed to change in between that
>>>> prevents you from merging the two together ?
>>
>> Thanks for pointing this out. I can merge acpi_boot_table_init() and
>> early_acpi_boot_init() together, but can not merge early_acpi_boot_init()
>> and acpi_boot_init() together.
>>
>> early_acpi_boot_init() and acpi_boot_init() was separated intentionally for
>> memory hotplug reasons. memory allocated in this stage can not be migrated
>> and cause memory hot-remove failed, in order to keep memory allocated
>> at base node (general NUMA node 0 in the system) at boot stage, we should
>> parse SRAT first before CPU is enumerated, does this make sense to you?
>
> Are you parsing the SRAT in this series to get memory info or memory is
> still initialized by DT even when system is supposed to be booted with ACPI
> (ie there is a valid ACPI root table ?)
>
> I have a hunch the latter is what's happening (and that's wrong, because
> memory information when kernel is booted through ACPI must be retrieved
> from UEFI - at least that's what has been defined), so I still see an early
> hook to initialize ACPI tables before paging_init() that has no use as the
> current patchset stands, please correct me if I am wrong.
Yes, currently memory is initialized by DT but getting memory map from 
UEFI is the matter of time (pending upstream process). Also, SRAT table 
is not parsing in this series but it will, and I think it plays the main 
role to put it before paging_init.

Regards,
Tomasz
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