linux-kernel - Re: [PATCH] x86, acpi: Handle lapic/x2apic entries in MADT

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Date:	Wed, 26 Aug 2015 19:49:28 +0200
From:	Lukasz Anaczkowski <lukasz.anaczkowski@...el.com>
To:	marc.zyngier@....com, lorenzo.pieralisi@....com,
	tomasz.nowicki@...aro.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, jason@...edaemon.net
Cc:	rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH] x86, acpi: Handle lapic/x2apic entries in MADT

Marc nad Lorenzo,

First of all appologies for breaking arm64 (again) and thank you for
debugging effort. I own you.

> - count is only incremented when max_entries != 0, as you noticed

You are right, sorry for that, it's fixed in v3.

> - With max_entries != 0, count now represent the sum of all matches
>  Is that expected?

I have no strong opinion on that one. All of the x86 ACPI entries
handling only checks for count < 0, or uses count from the
acpi_subtable_proc structure (and that's why I didn't noticed the
mainline breakage).
If you think it's not correct or less usable than other approach,
let me know.

> - The proc iteration stops after the first match. Why?

So, the initial implementation of the acpi_parse_entries accepted
single handler for the ACPI table. Now, with this change, assumption
is that different handlers for different tables/subtables are passed,
meaning only one can meet entry->type == proc[i].id condition.
mainline breakage). This approach saves one local varaible, but
I don't think this is ultimate argument :)

> - The test for max_entries is done inside the proc loop. Why?

That's obviously wrong in context of the overall wrong counting.

> [...] this should be documented and agreed upon.

I've added description with assumptions. Again, if you think it's
not correct, let me know.

Tomasz Nowicki wrote:
> should acpi_table_parse_entries suppose to be removed above?

Thanks for pointing this out. I've missed implementation of
acpi_table_parse_entries when was backporting initial patch.
I've added it back.

Cheers,
Lukasz

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