Re: [PATCH V7 4/5] arm64: apei: implement arch_apei_get_mem_attributes()

[Matt Fleming <matt.fleming@intel.com>]

On Fri, 2015-07-24 at 17:26 +0100, Will Deacon wrote:
> On Fri, Jul 24, 2015 at 05:21:49PM +0100, Catalin Marinas wrote:
> > On Fri, Jul 24, 2015 at 03:57:08PM +0100, Will Deacon wrote:
> > > On Tue, Jul 21, 2015 at 10:59:19PM +0100, Jonathan (Zhixiong) Zhang wrote:
> > > > diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> > > > +static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
> > > > +{
> > > > +	pgprot_t prot;
> > > > +
> > > > +	prot = efi_mem_attributes(addr);
> > > > +	if (prot & EFI_MEMORY_UC)
> > > > +		return PROT_DEVICE_nGnRnE;
> > > > +	if (prot & EFI_MEMORY_WC)
> > > > +		return PROT_NORMAL_NC;
> > > 
> > > Can we not use pgprot_noncached and pgprot_writecombine for these two?
> > 
> > Actually, why do we even use pgprot_t for prot here? EFI_MEMORY_* don't
> > have anything to do with the arch-specific pgprot_t.
> 
> Good point; the pgprot_t confused me, so my suggestion is much use after
> ll. We're better off with a u64 to avoid further confusion.

Isn't the whole point of arch_apei_get_mem_attribute() to turn an
arch-independent memory attribute (EFI_MEMORY_*) into an arch-specific
value to pass to ioremap_page_range()?

I don't see how you can do that any other way than by using pgprot_t.

Really, the problem here is that ioremap_page_caller() has no notion of
"map this range in a firmware-compatible manner". If we could do, for
example,

	ioremap_page_range(vaddr, vend, paddr, PAGE_FW_COMPAT);

that would allow the innards of the arch-ioremap to figure out exactly
how to map this range so that the firmware could access it coherently.

I suggested this previously but it didn't gain any traction.