Re: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64

From: Catalin Marinas <catalin.marinas@arm.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "msalter@redhat.com" <msalter@redhat.com>,
	Mark Rutland <Mark.Rutland@arm.com>,
	Mark Langsdorf <mlangsdo@redhat.com>,
	"linaro-acpi@lists.linaro.org" <linaro-acpi@lists.linaro.org>,
	Will Deacon <Will.Deacon@arm.com>,
	"wangyijing@huawei.com" <wangyijing@huawei.com>,
	Rob Herring <robh@kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
	Timur Tabi <timur@codeaurora.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"grant.likely@linaro.org" <grant.likely@linaro.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@arm.com>,
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	Sudeep Holla <Sudeep.Holla@arm.com>,
	Olof Johansson <olof@lixom.net>
Subject: Re: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64
Date: Thu, 5 Feb 2015 10:59:45 +0000	[thread overview]
Message-ID: <20150205105945.GC18158@e104818-lin.cambridge.arm.com> (raw)
In-Reply-To: <CAKv+Gu-tqY4C0eaRvp5FAzx9PqOGMg+sFNzxr2f25omdJKr7JA@mail.gmail.com>

On Thu, Feb 05, 2015 at 10:47:23AM +0000, Ard Biesheuvel wrote:
> On 5 February 2015 at 10:41, Catalin Marinas <catalin.marinas@arm.com> wrote:
> > On Wed, Feb 04, 2015 at 06:58:14PM +0000, Mark Salter wrote:
> >> On Wed, 2015-02-04 at 17:57 +0000, Catalin Marinas wrote:
> >> > On Wed, Feb 04, 2015 at 04:08:27PM +0000, Mark Salter wrote:
> >> > > acpi_os_remap() is used to map ACPI tables. These tables may be in ram
> >> > > which are already included in the kernel's linear RAM mapping. So we
> >> > > need ioremap_cache to avoid two mappings to the same physical page
> >> > > having different caching attributes.
> >> >
> >> > What's the call path to acpi_os_ioremap() on such tables already in the
> >> > linear mapping? I can see an acpi_map() function which already takes
> >> > care of the RAM mapping case but there are other cases where
> >> > acpi_os_ioremap() is called directly. For example,
> >> > acpi_os_read_memory(), can it be called on both RAM and I/O?
> >>
> >> acpi_map() is the one I've seen.
> >
> > By default, if should_use_kmap() is not patched for arm64, it translates
> > to page_is_ram(); acpi_map() would simply use a kmap() which returns the
> > current kernel linear mapping on arm64.
> >
> >> I'm not sure about others.
> >
> > Question for the ARM ACPI guys: what happens if you implement
> > acpi_os_ioremap() on arm64 as just ioremap()? Do you get any WARN_ON()
> > (__ioremap_caller() checks whether the memory is RAM)?
> 
> Regardless of whether you hit any WARN_ON()s now,

Actually following the WARN_ON(), ioremap() returns NULL, so it may not
go entirely unnoticed.

> we still need to distinguish between MMIO ranges with device
> semantics, and ACPI or other tables whose data may not be naturally
> aligned all the time, and hence requiring memory semantics.
> acpi_os_ioremap() may be used for both, afaik

Is acpi_os_ioremap() called directly (outside acpi_map()) to map RAM
that already part of the kernel linear memory? If yes, then I agree that
we need to do such check.

Another question, can we distinguish, in the ACPI core code, whether the
mapping is for an ACPI table in RAM or some I/O space?

-- 
Catalin