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

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Date:	Thu, 9 Feb 2012 18:19:03 -0800
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Myron Stowe <mstowe@...hat.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, Feb 9, 2012 at 4:08 PM, Myron Stowe <mstowe@...hat.com> wrote:
> 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.

I dunno if you're comfortable with it, but you can always propose a
patch doing it how you think it should be done.  People are more apt
to respond to a concrete patch than to an abstract question about why
things are the way they are.

Bjorn
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