linux-kernel - Re: [patch v11 12/23] ARM64 / ACPI: Parse MADT for SMP initialization

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Date:	Thu, 26 Mar 2015 21:12:42 +0000
From:	Will Deacon <will.deacon@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Olof Johansson <olof@...om.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Ashwin Chaugule <ashwinc@...eaurora.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Robert Richter <rric@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Timur Tabi <timur@...eaurora.org>,
	"msalter@...hat.com" <msalter@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [patch v11 12/23] ARM64 / ACPI: Parse MADT for SMP initialization

On Thu, Mar 26, 2015 at 07:48:50PM +0000, Hanjun Guo wrote:
> On 2015年03月26日 23:15, Will Deacon wrote:
> > commit 8ef320319592693f4a6286d80df210fd47b3e356
> > Author: Will Deacon <will.deacon@....com>
> > Date:   Thu Mar 26 15:09:20 2015 +0000
> >
> >      ARM64 / ACPI: fix usage of acpi_map_gic_cpu_interface
> >
> >      acpi_parse_gic_cpu_interface calls acpi_map_gic_cpu_interface by both
> >      passing a 32-bit value in the u8 enabled parameter and then subsequently
> >      ignoring its return value.
> >
> >      Sort it out.
> >
> >      Reported-by: Catalin Marinas <catalin.marinas@....com>
> >      Signed-off-by: Will Deacon <will.deacon@....com>
> >
> > diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> > index cd60329da8c4..07649e413244 100644
> > --- a/arch/arm64/kernel/acpi.c
> > +++ b/arch/arm64/kernel/acpi.c
> > @@ -103,9 +103,12 @@ void __init __acpi_unmap_table(char *map, unsigned long size)
> >    *
> >    * Returns the logical cpu number which maps to MPIDR
> >    */
> > -static int __init acpi_map_gic_cpu_interface(u64 mpidr, u8 enabled)
> > +static int __init
> > +acpi_map_gic_cpu_interface(struct acpi_madt_generic_interrupt *processor)
> 
> How about just replace u8 with u32? This function has its purpose to
> be lived, on x86/ia64, ACPI core will get the physcal cpu ID via
> ACPI handle, then pass it to the arch specific mapping function
> to map the physcal cpu ID with logical cpu ID for the new added
> CPU, so when ACPI based CPU hot-plug is introduced on ARM64, we
> need to go back to that solution.

If/when that happens, we can change things then. Right now, this is a static
function with one caller. One step at a time, please.

> >   {
> >   	int i;
> > +	u64 mpidr = processor->arm_mpidr & MPIDR_HWID_BITMASK;
> > +	bool enabled = !!(processor->flags & ACPI_MADT_ENABLED);
> >
> >   	if (mpidr == INVALID_HWID) {
> >   		pr_info("Skip MADT cpu entry with invalid MPIDR\n");
> > @@ -178,11 +181,7 @@ acpi_parse_gic_cpu_interface(struct acpi_subtable_header *header,
> >   		return -EINVAL;
> >
> >   	acpi_table_print_madt_entry(header);
> > -
> > -	acpi_map_gic_cpu_interface(processor->arm_mpidr & MPIDR_HWID_BITMASK,
> > -		processor->flags & ACPI_MADT_ENABLED);
> > -
> > -	return 0;
> > +	return acpi_map_gic_cpu_interface(processor);
> 
> I don't think we need to return the error value here, in ACPI
> core, it will stop the MADT scanning once it returned the error
> value, but actually we can skip some disabled GICC (cpu) entries
> and find all the enabled ones in MADT, for example,
> 
> cpu0 entry, with flag enabled
> cpu1 entry, disabled  - if we return the error value, table scanning
>                          will stop
> cpu2 entry, enabled   - and this cpu will be ignored

Then send me a patch making acpi_map_gic_cpu_interface have a void return
type. Ignoring the return type is usually a good way to introduce subtle
bugs.

Will
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