linux-kernel - Re: [PATCH v3 1/7] acpi: Add early device probing infrastructure

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Date:	Mon, 5 Oct 2015 12:07:42 -0500
From:	Wei Huang <wei@...hat.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linaro-acpi@...ts.linaro.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/7] acpi: Add early device probing infrastructure



On 10/03/2015 05:04 AM, Marc Zyngier wrote:
> On Fri, 2 Oct 2015 16:06:05 -0500
> Wei Huang <wei@...hat.com> wrote:
> 
> Hi Wei,
> 
>> Hi Marc,
> 
> [...]
> 
>>> +struct acpi_probe_entry {
>>> +	__u8 id[ACPI_TABLE_ID_LEN];
>>> +	__u8 type;
>>> +	acpi_probe_entry_validate_subtbl subtable_valid;
>>> +	union {
>>> +		acpi_tbl_table_handler probe_table;
>>> +		acpi_tbl_entry_handler probe_subtbl;
>>> +	};
>>
>> Could we avoid using union for probe_table & probe_subtbl? The benefit is that we don't need to do function casting below and compiler can automatically check the correctness.
>>
>>> +	kernel_ulong_t driver_data;
>>> +};
>>> +
>>> +#define ACPI_DECLARE_PROBE_ENTRY(table, name, table_id, subtable, valid, data, fn)	\
>>> +	static const struct acpi_probe_entry __acpi_probe_##name	\
>>> +		__used __section(__##table##_acpi_probe_table)		\
>>> +		 = {							\
>>> +			.id = table_id,					\
>>> +			.type = subtable,				\
>>> +			.subtable_valid = valid,			\
>>> +			.probe_table = (acpi_tbl_table_handler)fn,	\
>>> +			.driver_data = data, 				\
>>> +		   }
>>> +
>>
>> Something like: 
>>
>> #define ACPI_DECLARE_PROBE_ENTRY(table, name, table_id, subtable, valid, data, fn, subfn)	\
>> 	static const struct acpi_probe_entry __acpi_probe_##name	\
>> 		__used __section(__##table##_acpi_probe_table)		\
>> 		 = {							\
>> 			.id = table_id,					\
>> 			.type = subtable,				\
>> 			.subtable_valid = valid,			\
>> 			.probe_table = fn,				\
>> 			.probe_subtbl = subfn,				\
>> 			.driver_data = data, 				\
>> 		   }
>>
>> Then in patch 3, you can define new entries as:
>>
>> IRQCHIP_ACPI_DECLARE(gic_v2, ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR,
>> 		     gic_validate_dist, ACPI_MADT_GIC_VERSION_V2,
>> 		     NULL, gic_v2_acpi_init);
>> IRQCHIP_ACPI_DECLARE(gic_v2_maybe, ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR,
>> 		     gic_validate_dist, ACPI_MADT_GIC_VERSION_NONE,
>> 		     NULL, gic_v2_acpi_init);
>>
> 
> That's exactly what I was trying to avoid. If you want to do that, do
> it in the IRQCHIP_ACPI_DECLARE macro, as there is strictly no need for
> this this NULL to appear here (MADT always matches by subtable).
> 
> Or even better, have two ACPI_DECLARE* that populate the probe entry in
> a mutually exclusive way (either probe_table is set and both
> valid/subtbl are NULL, or probe_table is NULL and the two other fields
> are set).

Yes, this approach would be sufficient. So users can clearly tell them
apart in terms of usage cases.

Thanks,
-Wei

> 
> Thanks,
> 
> 	M.
> 
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