linux-kernel - Re: ACPI early ioremap problems

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Date:	Sat, 19 Jan 2008 16:46:51 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>, venkatesh.pallipadi@...el.com,
	suresh.b.siddha@...el.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: ACPI early ioremap problems

On Sat, Jan 19, 2008 at 04:30:55PM +0100, Ingo Molnar wrote:
> > > that case it's a 64-bit early_ioremap() bug that we want to find 
> > > even if ACPI didnt use early_ioremap().
> > > 
> > > and this all runs before zap_low_mappings(), right?
> > 
> > No after. Since some time x86-64 does the equivalent of z_l_m() in 
> > head64(); this means before start_kernel and definitely before 
> > setup_arch which sets up ACPI.
> 
> that would mean early_ioremap() should switch to ioremap() after that 
> point. Could you try that, does it resolve the failure you are seeing? 

ioremap() does alloc_page and that won't work before 
paging_init(). Early ACPI scan is before paging_init() because
paging_init() needs node discovery at at least; which requires
some ACPI tables.

> Long-term we want to have a single, uniform ioremap() interface (on 
> 32-bit and 64-bit x86 as well) that can be used anytime, which just 
> switches to the right lowlevel method depending on how far we are into 
> the pagetable and memory subsystem bootstrap - instead of these more 
> fragile "can we now use early_ioremap() or should we already be using 
> ioremap()" usages.

I didn't think there were enough early/bt_ioremap() users for this
to be really worthwhile. The only code that does both I'm aware of
is the memory setup code.

-Andi

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