Subject: Re: [PATCH] [POWERPC] Port fixmap from x86 and use for kmap_atomic

From: "Gerhard Pircher" <[email-masked]>
Date: Sat, 19 Apr 2008 13:07:40 +0200

-------- Original-Nachricht --------
> Datum: Thu, 17 Apr 2008 21:57:05 -0500 (CDT)
> Von: Kumar Gala <[email-masked]>
> An: Paul Mackerras <[email-masked]>
> CC: [email-masked]
> Betreff: [PATCH] [POWERPC] Port fixmap from x86 and use for kmap_atomic

> The fixmap code from x86 allows us to have compile time virtual addresses
> that we change the physical addresses of at run time.
...
> +/*
> + * Here we define all the compile-time 'special' virtual
> + * addresses. The point is to have a constant address at
> + * compile time, but to set the physical address only
> + * in the boot process. We allocate these special addresses
> + * from the end of virtual memory (0xfffff000) backwards.
> + * Also this lets us do fail-safe vmalloc(), we
> + * can guarantee that these special addresses and
> + * vmalloc()-ed addresses never overlap.
I don't understand how highmem works, but I'm just interested to know, if
this implementation could conflict somehow with the non coherent DMA
implementation in dma-noncoherent.c (which uses address space from
0xff100000 to 0xff300000 for DMA memory).
On the other side could dma-noncoherent.c benefit from fixmaps so that it
isn't necessary to configure a start address for DMA allocations?

Thanks!

best regards,

Gerhard
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