linux-kernel - Re: [PATCH v8 09/21] ARM64 / ACPI: Disable ACPI if FADT revision is less than 5.1

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Date:	Wed, 4 Feb 2015 13:06:26 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....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>, Arnd Bergmann <arnd@...db.de>,
	Mark Rutland <Mark.Rutland@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"phoenix.liyi@...wei.com" <phoenix.liyi@...wei.com>,
	Timur Tabi <timur@...eaurora.org>,
	Ashwin Chaugule <ashwinc@...eaurora.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Mark Langsdorf <mlangsdo@...hat.com>,
	"wangyijing@...wei.com" <wangyijing@...wei.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH v8 09/21] ARM64 / ACPI: Disable ACPI if FADT revision is
 less than 5.1

On Wed, Feb 04, 2015 at 09:38:25AM +0000, Hanjun Guo wrote:
> On 2015年02月04日 01:20, Catalin Marinas wrote:
> > On Mon, Feb 02, 2015 at 12:45:37PM +0000, Hanjun Guo wrote:
> >> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> >> index afe10b4..b9f64ec 100644
> >> --- a/arch/arm64/kernel/acpi.c
> >> +++ b/arch/arm64/kernel/acpi.c
> >> @@ -13,6 +13,8 @@
> >>    *  published by the Free Software Foundation.
> >>    */
> >>
> >> +#define pr_fmt(fmt) "ACPI: " fmt
> >> +
> >>   #include <linux/acpi.h>
> >>   #include <linux/bootmem.h>
> >>   #include <linux/cpumask.h>
> >> @@ -49,10 +51,32 @@ void __init __acpi_unmap_table(char *map, unsigned long size)
> >>   	early_memunmap(map, size);
> >>   }
> >>
> >> +static int __init acpi_parse_fadt(struct acpi_table_header *table)
> >> +{
> >> +	struct acpi_table_fadt *fadt = (struct acpi_table_fadt *)table;
> >> +
> >> +	/*
> >> +	 * Revision in table header is the FADT Major revision, and there
> >> +	 * is a minor revision of FADT which was introduced by ACPI 5.1,
> >> +	 * we only deal with ACPI 5.1 or newer revision to get GIC and SMP
> >> +	 * boot protocol configuration data, or we will disable ACPI.
> >> +	 */
> >> +	if (table->revision > 5 ||
> >> +	    (table->revision == 5 && fadt->minor_revision >= 1))
> >> +		return 0;
> >> +
> >> +	pr_warn("Unsupported FADT revision %d.%d, should be 5.1+, will disable ACPI\n",
> >> +		table->revision, fadt->minor_revision);
> >> +	disable_acpi();
> >> +
> >> +	return -EINVAL;
> >> +}
> >> +
> >>   /*
> >>    * acpi_boot_table_init() called from setup_arch(), always.
> >>    *	1. find RSDP and get its address, and then find XSDT
> >>    *	2. extract all tables and checksums them all
> >> + *	3. check ACPI FADT revision
> >>    *
> >>    * We can parse ACPI boot-time tables such as MADT after
> >>    * this function is called.
> >> @@ -64,8 +88,16 @@ void __init acpi_boot_table_init(void)
> >>   		return;
> >>
> >>   	/* Initialize the ACPI boot-time table parser. */
> >> -	if (acpi_table_init())
> >> +	if (acpi_table_init()) {
> >> +		disable_acpi();
> >> +		return;
> >> +	}
> >> +
> >> +	if (acpi_table_parse(ACPI_SIG_FADT, acpi_parse_fadt)) {
> >> +		/* disable ACPI if no FADT is found */
> >>   		disable_acpi();
> >> +		pr_err("Can't find FADT\n");
> >> +	}
> >>   }
> >
> > It looks fine to call disable_acpi() here but a bit weird to call it
> > again in acpi_parse_fadt(). I guess that's because acpi_table_parse()
> > ignores the return value of the handler() call. I think it's better to
> > fix the core code (can be an additional patch on top of this series).
> 
> I checked all the code calling acpi_table_parse() and I found that it
> will be no functional change if we return the value of handler(), but
> I need Rafael's confirm on it.

Are you sure ? All calls to acpi_table_parse() that checks the return
value are affected. I guess that depends on what an error return from
the handler means, from acpi_table_parse():

* Return 0 if table found, -errno if not.

So, if table is found but parsing fails that acpi_table_parse()
signature should be changed if the handler barfs with an error and
it is propagated. Still, I share Catalin's comment.

Have you thought about getting the FADT through:

acpi_get_table_with_size()

and check the revision there instead of going through acpi_table_parse()
for that ?

I wonder if the revision information is not already available without
needing to retrieve the FADT again.

On top of that, this patch should be squashed, I have a feeling that
between patch 4 and 9, there is a window where ACPI versions predating
5.1 are ok on arm64, which is not the case. I do not think that's a
bisectable issue, but keep this in mind please.

Thanks,
Lorenzo
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