From: Timur Tabi <timur@freescale.com>
To: Dan Malek <ppc6dev@digitaldans.com>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: minimum guaranteed alignment of dma_alloc_coherent?
Date: Mon, 7 Feb 2011 09:13:44 -0600 [thread overview]
Message-ID: <4D500C28.7000704@freescale.com> (raw)
In-Reply-To: <9E25355F-62B4-46A3-9991-FDE89FB6B862@digitaldans.com>
Dan Malek wrote:
> So, I did a little research. It appears in the case of PowerPC,
> the GFP_DMA can change the way the allocation operates.
> Since the coherent allocator works with pages of memory,
> in the case of a system with highmem, not using GFP_DMA
> could hand you a physical page out of the highmem pool.
I think that's true only if SWIOTLB is enabled. dma_direct_alloc_coherent()
does this:
/* ignore region specifiers */
flag &= ~(__GFP_HIGHMEM);
> This behavior is modified if you specify a restricted DMA
> mask for the device. In this case, dma_alloc_coherent
> will force GFP_DMA on your behalf (on PowerPC).
Isn't it required for all callers of dma_alloc_coherent to specify a mask (via
dma_set_mask) first?
--
Timur Tabi
Linux kernel developer at Freescale
--
Timur Tabi
Linux kernel developer at Freescale
next prev parent reply other threads:[~2011-02-07 15:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-05 0:14 minimum guaranteed alignment of dma_alloc_coherent? Timur Tabi
2011-02-05 1:09 ` Dan Malek
2011-02-05 2:04 ` Tabi Timur-B04825
2011-02-05 2:56 ` Dan Malek
2011-02-07 15:13 ` Timur Tabi [this message]
2011-03-29 0:32 ` Benjamin Herrenschmidt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4D500C28.7000704@freescale.com \
--to=timur@freescale.com \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=ppc6dev@digitaldans.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.