linux-kernel - Re: [PATCH V5 3/4] arm64: apei: implement arch_apei_get_mem

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Message-ID: <20150717094314.GE18994@arm.com>
Date:	Fri, 17 Jul 2015 10:43:14 +0100
From:	Will Deacon <will.deacon@....com>
To:	"Zhang, Jonathan Zhixiong" <zjzhang@...eaurora.org>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"fu.wei@...aro.org" <fu.wei@...aro.org>,
	"al.stone@...aro.org" <al.stone@...aro.org>,
	"bp @ alien8 . de Matt Fleming" <matt.fleming@...el.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH V5 3/4] arm64: apei: implement
 arch_apei_get_mem_attributes()

On Fri, Jul 17, 2015 at 02:37:00AM +0100, Zhang, Jonathan Zhixiong wrote:
> On 7/16/2015 10:18 AM, Will Deacon wrote:
> > On Wed, Jul 15, 2015 at 01:31:55AM +0100, Jonathan (Zhixiong) Zhang wrote:
> >> +pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
> >> +{
> >> +	if (efi_mem_attributes(addr) & EFI_MEMORY_UC)
> >> +		return PROT_DEVICE_nGnRE;
> >> +	else
> >> +		return PAGE_KERNEL;
> >> +}
> >
> > Do we really need a new file and out-of-line call for this?
> We have a choice of either adding this function to
> arch/arm64/kernel/acpi.c, or creating
> arch/arm64/kernel/apei.c. As we continue to work on firmware first
> HW error handling for arm64, more arm64 specific APEI related functions
> may need to be implemented, thus I think it would be good to create
> arch/arm64/kernel/apei.c. That being said, to date we have found
> the needs to have only two arm64 specific APEI related functions.
> The other one can be found in LEG kernel, through this commit:
>    aa2d69c88b27 ACPI, APEI, ARM64: APEI initial support for aarch64
> My understanding is that Linaro will work on to upstream that commit. I
> do not strongly prefer either choice.
> 
> When APEI ghes driver maps the memory region that has error record
> updated by firmware, it executes in IRQ, timer or SEA handler. Since
> ioremap() can not be used in atomic context, so APEI implements a
> special version of atomic ioremap function calling ioremap_page_range().
> On the other hand, x86 and ARM64 have different ways to define pgprot_t
> for page that needs to be accessed with uncached property. x86 defines
> PAGE_KERNEL_NOCACHE, while arm64 defines PROT_DEVICE_nGnRE. Therefore
> arch specific implementation is needed.
> There are other ways to achieve such needs. V3 of this
> patch set tried another way [1]. I think the current way makes the most
> sense, since it made generic APEI code to stay generic (no knowledge
> about EFI, no arch dependent ifdefs).

I understand what you're doing and my concern was much simpler than you
seem to imagine. Put another way: why can't arch_apei_get_mem_attribute
be a static inline in a header file (like acpi_os_ioremap in asm/acpi.h)?

Will
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