linux-kernel - Re: when to switch from early

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Date:	Tue, 23 Oct 2012 13:54:31 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Olaf Hering <olaf@...fle.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: when to switch from early_ioremap to ioremap

On Tue, Oct 23, 2012 at 12:42 PM, Olaf Hering <olaf@...fle.de> wrote:
>
> To obtain an address to a PFN in init_hypervisor_platform (called from
> arch/x86/kernel/setup.c:setup_arch) I use early_ioremap. Later the
> address to that PFN needs to be obtained with ioremap, and early_iounmap
> needs to be called on the first address.
>
> When is the time to obtain and use the new pointer, and to release to
> old pointer? Right now I do that in the pci-device setup code, which
> happens to work. Unfortunately early_ioremap is not mentioned in
> Documentation/, hence the question.

usually early_ioremap is used in this way:
map it and check it and unmap it. and some time you could back up it
before unmap.

you should only use early_iomap and early_memmap during SYSTEM_BOOTING

and check_early_ioremap_leak in late_initcall will check if all early
one get unmapped.

for 32bit, there is more requirement: you can not cross init_memory_mapping.
    early_ioremap_page_table_range_init/early_ioremap_reset will be
called in init_memory_mapping.

Also early_ioremap has slot limitation: 4. and you should not hold one
slot too long, otherwise other users could
have problem to reach the limit.

Yinghai
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