linux-kernel - Re: DMA using data buffer vmapped in kernel space

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Message-Id: <201003061407.12698.thomas@koeller.dyndns.org>
Date:	Sat, 6 Mar 2010 14:07:12 +0100
From:	Thomas Koeller <thomas@...ller.dyndns.org>
To:	"Russell King - ARM Linux" <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: DMA using data buffer vmapped in kernel space

Am Donnerstag, 4. März 2010 22:36:34 schrieb Russell King - ARM Linux:
> Cache maintainence is done using virtual addresses for L1, and
> physical addresses for L2.  There's the need for virtual addresses
> to be translatable to physical addresses, which is only true for
> the kernel direct mapped region (pages between PAGE_OFFSET and
> high_memory).

Isn't the mapping created by vmap() sufficient for the virt/phys
translation? In which way is this case different from a buffer
passed in from user space, where the constituent pages are not
in the directly mapped kernel region either?

tk

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