linux-kernel - Re: [PATCH] ACPI: Fix logic for removing mappings in 'acpi

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Date:	Thu, 09 Feb 2012 17:08:38 -0700
From:	Myron Stowe <mstowe@...hat.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Myron Stowe <myron.stowe@...hat.com>, lenb@...nel.org,
	linux-acpi@...r.kernel.org, ying.huang@...el.com,
	tony.luck@...el.com, trenn@...e.de, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: [PATCH] ACPI: Fix logic for removing mappings in 'acpi_unmap'

On Thu, 2012-02-09 at 08:42 -0800, Bjorn Helgaas wrote:
> On Thu, Feb 9, 2012 at 8:36 AM, Myron Stowe <myron.stowe@...hat.com> wrote:
> > From: Myron Stowe <mstowe@...hat.com>
> >
> > Make sure the removal of mappings uses the same logic that put the
> > mappings in place.
> >
> > Signed-off-by: Myron Stowe <myron.stowe@...hat.com>
> > ---
> >
> >  drivers/acpi/osl.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> > index 412a1e0..5aef087 100644
> > --- a/drivers/acpi/osl.c
> > +++ b/drivers/acpi/osl.c
> > @@ -347,7 +347,7 @@ static void acpi_unmap(acpi_physical_address pg_off, void __iomem *vaddr)
> >        unsigned long pfn;
> >
> >        pfn = pg_off >> PAGE_SHIFT;
> > -       if (page_is_ram(pfn))
> > +       if (should_use_kmap(pfn))
> >                kunmap(pfn_to_page(pfn));
> >        else
> >                iounmap(vaddr);
> >
> 
> Whatever happened to the question of why we have arch-specific
> ioremap() behavior?  It's good to make map/unmap symmetric, but it'd
> be better to get rid of the ioremap/kmap hack.

+cc ingo

We never received any explanation for why ioremap() failed for Ying with
RAM on x86.  Last I saw Ying asked Ingo for some input here but there
was never any reply -
http://marc.info/?l=linux-acpi&m=132788392604738&w=2

I like your idea of possibly changing ioremap's implementation so that
it would handle requests related to RAM - by using kmap() internally
when necessary - so that a *user* wouldn't need to care what
architecture we're on.  I, however, feel like I don't have enough
experience with the memory management subsystem to know if such a tactic
would fly or not so was uncomfortable proceeding along those lines.  As
a result, I just wanted to get this in for the meantime.

Myron

> 
> Bjorn


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