Message-ID: <20140124153557.GB23274@e102568-lin.cambridge.arm.com>
Date:	Fri, 24 Jan 2014 15:35:57 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>
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 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.

> >
> >> +
> >>   #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.

[...]

> >> +
> >> +	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?
> 
> 
> >
> >> +
> >> +	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.

Thanks,
Lorenzo

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