Date:	Sat, 25 Jan 2014 00:02:28 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Olof Johansson <olof@...om.net>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Rob Herring <robh@...nel.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Arnd Bergmann <arnd@...db.de>,
	"patches@...aro.org" <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>
Subject: Re: [PATCH 10/20] ARM64 / ACPI: Enumerate possible/present CPU set
 and map logical cpu id to APIC id

On 2014年01月24日 23:35, Lorenzo Pieralisi wrote:
> On Fri, Jan 24, 2014 at 02:37:28PM +0000, Hanjun Guo wrote:
>> Hi Lorenzo,
>>
>> On 2014?01?22? 23:53, Lorenzo Pieralisi wrote:
>>> On Fri, Jan 17, 2014 at 12:25:04PM +0000, Hanjun Guo wrote:
>>>
>>> [...]
>>>
>>>> +/* map logic cpu id to physical GIC id */
>>>> +extern int arm_cpu_to_apicid[NR_CPUS];
>>>> +#define cpu_physical_id(cpu) arm_cpu_to_apicid[cpu]
>>> Sudeep already commented on this, please update it accordingly.
>> Actually after some careful review of the ACPI code, I can't
>> update it as MPIDR here.
>>
>> MPIDR can be the ACPI uid and NOT the GIC id, the mapping
>> of them are something like this in ACPI driver now:
>>
>> logic cpu id <---> APIC Id (GIC ID) <---> ACPI uid (MPIDR on ARM)
>> but not logic cpu id <---> ACPI uid directly, you can refer to
>> the code of processor_core.c
>>
>> So here I can only map GIC id to logical cpu id.
> On ARM platforms GIC CPU IF id is probeable, you do not need to parse
> it (ie it is not information that you will find in DT). Please have a look
> at drivers/irqchip/irq-gic.c.
>
> We have to understand what's really required and when in ACPI, or to put it
> differently, why cpu_physical_id(cpu) is required and at what time at
> boot, I will have a look on my side too.

Me too :)

>
>>>> +
>>>>    #else	/* !CONFIG_ACPI */
>>>>    #define acpi_disabled 1		/* ACPI sometimes enabled on ARM */
>>>>    #define acpi_noirq 1		/* ACPI sometimes enabled on ARM */
>>>> diff --git a/drivers/acpi/plat/arm-core.c b/drivers/acpi/plat/arm-core.c
>>>> index 8ba3e6f..1d9b789 100644
>>>> --- a/drivers/acpi/plat/arm-core.c
>>>> +++ b/drivers/acpi/plat/arm-core.c
>>>> @@ -31,6 +31,7 @@
>>>>    #include <linux/smp.h>
>>>>    
>>>>    #include <asm/pgtable.h>
>>>> +#include <asm/cputype.h>
>>>>    
>>>>    /*
>>>>     * We never plan to use RSDT on arm/arm64 as its deprecated in spec but this
>>>> @@ -52,6 +53,13 @@ EXPORT_SYMBOL(acpi_pci_disabled);
>>>>     */
>>>>    static u64 acpi_lapic_addr __initdata;
>>> Is this variable actually needed ?
>> Yes, needed for GIC initialization.
>>
>>>>    
>>>> +/* available_cpus here means enabled cpu in MADT */
>>>> +static int available_cpus;
>>> Ditto.
>>>
>>>> +
>>>> +/* Map logic cpu id to physical GIC id (physical CPU id). */
>>>> +int arm_cpu_to_apicid[NR_CPUS] = { [0 ... NR_CPUS-1] = -1 };
>>>> +static int boot_cpu_apic_id = -1;
>>> Do we need all these variables ? I think we should reuse cpu_logical_map
>>> data structures for that, it looks suspiciously familiar.
>> MPIDR is the different part. if we use MPIDR as GIC id, i think
>> we can reuse cpu_logical_map, but Sudeep suggested not
>> use MPIDR as GIC id.
> It is not about *reusing* cpu_logical_map, it is about setting it up
> properly. cpu_logical_map must be initialized by ACPI for the spin table
> method to work properly (and PSCI too).
>
> And yes, cpu_physical_id(cpu) is expected to be the GIC CPU IF id on
> ARM, at least it looks like, I had a look too. But this does not change
> anything as far as cpu_logical_map is concerned, it must contain a list
> of MPIDRs in the system and must be retrieved via ACPI, not DT CPU nodes
> when ACPI is used for booting.
>
> I will have a further look, since this discrepancy is annoying.

Thank you for doing this, I will look that too.

>
> [...]
>
>>>> +
>>>> +	available_cpus++;
>>>> +
>>> Is available_cpus != num_possible_cpus() ? It does not look like hence
>>> available_cpus can go.
>> No, possible cpus include available cpus and disabled cpus
>> this is useful for ACPI based CPU hot-plug features.
>>
>>>> +	/* allocate a logic cpu id for the new comer */
>>>> +	if (boot_cpu_apic_id == id) {
>>>> +		/*
>>>> +		 * boot_cpu_init() already hold bit 0 in cpu_present_mask
>>>> +		 * for BSP, no need to allocte again.
>>>> +		 */
>>>> +		cpu = 0;
>>>> +	} else {
>>>> +		cpu = cpumask_next_zero(-1, cpu_present_mask);
>>>> +	}
>>>> +
>>>> +	/* map the logic cpu id to APIC id */
>>>> +	arm_cpu_to_apicid[cpu] = id;
>>>> +
>>>> +	set_cpu_present(cpu, true);
>>>> +	set_cpu_possible(cpu, true);
>>> This is getting nasty. Before adding this patch and previous ones we
>>> need to put in place a method for the kernel to make a definite choice between
>>> ACPI and DT and stick to that. We can't initialize the logical map twice
>>> (which will happen if your DT has valid cpu nodes and a chosen node pointing
>>> to proper ACPI tables) or even having some entries initialized from DT and
>>> others by ACPI. It is a big fat no-no, please update the series accordingly.
>> really good catch here :)
>> so the problem here is that should we use both ACPI and DT in one system?

I think Mark had a clear answer about this :) (Answer for my self)

>>
>>
>>>> +
>>>> +	return cpu;
>>>> +}
>>>> +
>>>>    static int __init
>>>>    acpi_parse_gic(struct acpi_subtable_header *header, const unsigned long end)
>>>>    {
>>>> @@ -144,6 +201,16 @@ acpi_parse_gic(struct acpi_subtable_header *header, const unsigned long end)
>>>>    
>>>>    	acpi_table_print_madt_entry(header);
>>>>    
>>>> +	/*
>>>> +	 * We need to register disabled CPU as well to permit
>>>> +	 * counting disabled CPUs. This allows us to size
>>>> +	 * cpus_possible_map more accurately, to permit
>>>> +	 * to not preallocating memory for all NR_CPUS
>>>> +	 * when we use CPU hotplug.
>>>> +	 */
>>>> +	acpi_register_gic_cpu_interface(processor->gic_id,
>>>> +			processor->flags & ACPI_MADT_ENABLED);
>>>> +
>>>>    	return 0;
>>>>    }
>>>>    
>>>> @@ -186,6 +253,19 @@ static int __init acpi_parse_madt_gic_entries(void)
>>>>    		return count;
>>>>    	}
>>>>    
>>>> +#ifdef CONFIG_SMP
>>>> +	if (available_cpus == 0) {
>>>> +		pr_info(PREFIX "Found 0 CPUs; assuming 1\n");
>>>> +		arm_cpu_to_apicid[available_cpus] =
>>>> +			read_cpuid_mpidr() & MPIDR_HWID_BITMASK;
>>>> +		available_cpus = 1;	/* We've got at least one of these */
>>>> +	}
>>> I'd rather check the MADT for at least the boot cpu to present, if it is
>>> not ACPI tables are horribly buggy and the kernel should barf on that.
>>>
>>>> +#endif
>>>> +
>>>> +	/* Make boot-up look pretty */
>>>> +	pr_info("%d CPUs available, %d CPUs total\n", available_cpus,
>>>> +		total_cpus);
>>> Ok, now, how can we use the "disabled" CPUs == (total_cpus - available_cpus) ?
>> For cpus can be hot-added later when system is running.
> I do not see any usage in the patchset and certainly those variables are
> not used in this patch, apart from printing messages whose usefulness is
> debatable. If, as you say, you are using those variables for something
> else, please add code in the patch where they are introduced for it to be
> self-contained and to simplify the review.

ah, yes. although my ACPI based CPU hot-plug patch is ready, but need
this patch set goes in first and then send them out.

I agree with you, will try to update this patch.

Thanks
Hanjun
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