Re: driver mmap implementation for memory allocated with pci_alloc_consistent()?

From: Leon Woestenberg <leon.woestenberg@gmail.com>
To: "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	linux-mm@kvack.org
Subject: Re: driver mmap implementation for memory allocated with pci_alloc_consistent()?
Date: Thu, 19 May 2011 03:34:55 +0200	[thread overview]
Message-ID: <BANLkTik2UvgpsW-y_gZki_06KGGss+XABA@mail.gmail.com> (raw)
In-Reply-To: <1305767957.2375.117.camel@sli10-conroe>

Hello,

On Thu, May 19, 2011 at 3:19 AM, Shaohua Li <shaohua.li@intel.com> wrote:
> On Wed, 2011-05-18 at 21:02 +0800, Leon Woestenberg wrote:
> why use pci_alloc_consistent? you can allocate pages and mmap it to
> userspace. when you want to do dma, you can use pci_map_page to get dma
> address for the pages and do whatever.
>
Thanks for thinking along.

I need contiguous memory in this case.  But yes, I have just found out
that __get_free_pages() with pci_map_single()  does work with my
mmap() fault() handler.
See my other thread with the code posted.

I just want to understand how this would work with
pci_alloc_consistent(), as that is the generic interface for PCI
drivers.

Note that the latter provides consistent / coherent mapping, whereas
pci_map_single() does not in general.   On x86 it probably is the same
due to bus-snooping (right?).

Regards,
--
Leon

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