From: Takashi Iwai <tiwai@suse.de>
To: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Subject: Inconsistent pgprot between dma_alloc_coherent() and dma_mmap_cohernet()
Date: Mon, 10 Nov 2014 15:33:00 +0100 [thread overview]
Message-ID: <s5htx27p1lv.wl-tiwai@suse.de> (raw)
Hi,
I noticed using dma_mmap_coherent() on pages allocated via
dma_alloc_coherent() results in a warning on x86:
map pfn RAM range req uncached-minus for [mem 0x21d500000-0x21d51ffff], got write-back
which comes from arch/x86/mm/pat.c.
Looking at the code, it seems that dma_mmap_coherent() blindly assumes
that the pages are with pgprot_noncached(), but on x86, it's obviously
not. Maybe some other archs have the same problem.
How should we fix this? Defining a new pgprot_xxx(), and falling back
to pgprot_noncached if undefined? Or is it just x86 and do it only
there?
thanks,
Takashi
reply other threads:[~2014-11-10 14:33 UTC|newest]
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