From: Michael Buesch <mb@bu3sch.de>
To: Greg KH <greg@kroah.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>,
Eric Valette <eric.valette@free.fr>,
FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
"John W. Linville" <linville@tuxdriver.com>,
linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-usb@vger.kernel.org, Hin-Tak Leung <hintak.leung@gmail.com>
Subject: Re: DMA debug trace pointing to rtl8187
Date: Sat, 9 May 2009 22:19:39 +0200 [thread overview]
Message-ID: <200905092219.40216.mb@bu3sch.de> (raw)
In-Reply-To: <20090509192959.GA1842@kroah.com>
On Saturday 09 May 2009 21:29:59 Greg KH wrote:
> On Sat, May 09, 2009 at 12:29:27PM -0500, Larry Finger wrote:
> > I think there is a second problem that John's fix does not treat. Although the
> > buffer is removed from the stack, there is no assurance that the buffer obtained
> > with kmalloc() is reachable by DMA. This case will be triggered if the USB
> > adapter does 32-bit DMA and the system has more than 4 GB RAM.
In practice this does not hit, because such systems' kmalloc does not return
memory above 4G (i386) _or_ the DMA mapping functions take care of bounce buffering
or I/O-remapping (should be true for all other arches).
So if the device is able to do DMA with addresses >=32bit it should be fine, provided
it correctly sets the DMA mask.
> Memory returned by kmalloc will always be able to be DMAable. If not,
> we have lots of problems :)
True for sane devices.
False for devices like Broadcom HND-DMA, which should only be used to slap thy hw engineers.
--
Greetings, Michael.
prev parent reply other threads:[~2009-05-09 20:21 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <49FDB9F8.3080400@free.fr>
[not found] ` <20090506133131F.fujita.tomonori@lab.ntt.co.jp>
[not found] ` <4A012FC8.3020304@free.fr>
2009-05-06 6:45 ` DMA debug trace pointing to rtl8187 Greg KH
2009-05-06 18:02 ` [RFT] rtl8187: use DMA-aware buffers with usb_control_msg John W. Linville
2009-05-08 23:20 ` Hin-Tak Leung
2009-05-09 9:38 ` Eric Valette
2009-05-09 13:57 ` Greg KH
2009-05-09 15:50 ` John W. Linville
2009-05-09 16:35 ` Greg KH
2009-05-09 21:24 ` Larry Finger
2009-05-11 13:20 ` John W. Linville
2009-05-11 22:23 ` Hin-Tak Leung
2009-05-06 18:03 ` DMA debug trace pointing to rtl8187 John W. Linville
2009-05-09 17:29 ` Larry Finger
2009-05-09 17:46 ` Eric Valette
2009-05-09 19:22 ` Eric Valette
2009-05-09 19:29 ` Greg KH
2009-05-09 20:19 ` Michael Buesch [this message]
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