linux-kernel - Re: [PATCH 2/3] dma: override "dma_flags_set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070821193522.GD5592@sgi.com>
Date:	Tue, 21 Aug 2007 12:35:22 -0700
From:	akepner@....com
To:	Jes Sorensen <jes@....com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>, rdreier@...co.com,
	linux-ia64 <linux-ia64@...r.kernel.org>
Subject: Re: [PATCH 2/3] dma: override "dma_flags_set_dmaflush" for sn-ia64


> I'm a little concerned about changing the API for the dma_ foo
> functions, which are defined cross platform. If you want to change
> that, I think it will require updating the documentation explaining
> it.....

What do you think of the following? (And is there anyone else 
I should be cc-ing for review?)


Document semantics of dma_flags_set_dmaflush()

Signed-off-by: Arthur Kepner <akepner@....com>
--
 DMA-API.txt |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+)

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index cc7a8c3..e117b72 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -392,6 +392,28 @@ Notes:  You must do this:
 
 See also dma_map_single().
 
+int
+dma_flags_set_dmaflush(int dir)
+
+Amend dir (one of the enum dma_data_direction values), with a platform-
+specific "dmaflush" attribute. Unless the platform supports "posted DMA" 
+this is a no-op. 
+
+On platforms that support posted DMA, dma_flags_set_dmaflush() causes 
+device writes to the associated memory region to flush in-flight DMA. 
+This can be important, for example, when (DMA) writes to the memory 
+region indicate that DMA of data is complete. If DMA of data and DMA of 
+the completion indication race, as they can do when the platform supports 
+posted DMA, then the completion indication may arrive in host memory 
+ahead of some data.
+
+To prevent this, you might map the memory region used for completion 
+indications as follows:
+
+	int count, flags = dma_flags_set_dmaflush(DMA_BIDIRECTIONAL);
+	.....
+	count = dma_map_sg(dev, sglist, nents, flags);
+
 
 Part II - Advanced dma_ usage
 -----------------------------
-- 
Arthur

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/