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

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Date:	Fri, 27 Mar 2015 07:01:10 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Will Deacon <will.deacon@....com>
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 2015年03月27日 05:12, Will Deacon wrote:
> 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.

OK, I will, and I will cleanup the comments for this function too.

Need some sleep first...

Thanks
Hanjun
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