From: Jussi Kivilinna <jussi.kivilinna@iki•fi>
To: Ming Lei <tom.leiming@gmail•com>
Cc: linux-usb@vger•kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
Network Development <netdev@vger•kernel.org>
Subject: Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
Date: Sat, 15 Jun 2013 13:19:10 +0300 [thread overview]
Message-ID: <51BC3F9E.3010605@iki.fi> (raw)
In-Reply-To: <CACVXFVM4TsS-_qK_w01oajV1XcA_+OF8xdTX2xjjxOTFNAo6Sw@mail.gmail.com>
On 15.06.2013 10:41, Ming Lei wrote:
> Cc: netdev
>
> On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna <jussi.kivilinna@iki•fi> wrote:
>> Appearently some out-of-tree USB host drivers do not handle DMA alignment for
>
> Looks these host drivers have to face the fact that the transfer buffer is often
> DMA non-aligned from network device drivers(in fact, the buffer is from
> network protocol stack), if you run usbnet, then you will get the added warning
> immediately.
>
Yes, getting warning immediately, but once, and blaming host driver seems ok.
>> URB buffers and let core/hcd.c to do the mapping on architectures that have
>> minimum DMA alignment requirements. This leads to random memory corruptions
>> and crashes when using USB device drivers that use unaligned URB buffers.
>
> Maybe you should check the dma mapping/unmapping implementation of
> the arch, non-aligned buffer should have be covered by the API easily.
>
> Also USB Host controller should have supported non-aligned DMA buffer.
>From what I found, there was some discussion about these issues around 2010:
http://lists.infradead.org/pipermail/linux-arm-kernel/2010-August/022983.html
To me, it seems that non-aligned buffers cannot be easily handled by all archs
at dma mapping/unmapping phase and that HCD driver should do the alignment on
archs that set ARCH_DMA_MINALIGN. For example, ehci_tegra does copy unaligned
transfer buffers to temporary aligned buffers before letting them to USB core.
>
>>
>> Instead of fixing host drivers, users end up posting bug reports against
>> those USB device drivers that use unaligned buffers for URB; such as with
>> rtl8192cu (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631).
>
> Not only rtl8192cu driver, all USB network device drivers have the problem.
>
>>
>> Patch makes this issue more visible at core level, and hopefully gives hint
>> for future hcd driver implementors about this problem.
>
> So please find the root cause first, and don't add the noise now.
I think the root cause is that host driver is letting pass non-aligned buffers
to core on archs that have ARCH_DMA_MINALIGN set.
The warning given just before such unaligned buffer is passed to dma_map_single,
which requires ARCH_DMA_MINALIGN alignment. This seems reasonable to me.
-Jussi
>
>
> Thanks,
>
next prev parent reply other threads:[~2013-06-15 10:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20130614133803.25747.98705.stgit@localhost6.localdomain6>
[not found] ` <20130614133803.25747.98705.stgit-bi+AKbBUZKagILUCTcTcHdKyNwTtLsGr@public.gmane.org>
2013-06-15 7:41 ` [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped Ming Lei
2013-06-15 10:19 ` Jussi Kivilinna [this message]
[not found] ` <51BC3F9E.3010605-X3B1VOXEql0@public.gmane.org>
2013-06-15 12:07 ` Ming Lei
[not found] ` <CACVXFVMe9fgdiDTRC0rWvwZJM8aT7AZY8Q1MwiOTc4ks0PQPOg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-06-15 13:10 ` Jussi Kivilinna
2013-06-15 13:22 ` Jussi Kivilinna
[not found] ` <51BC6A96.7030707-X3B1VOXEql0@public.gmane.org>
2013-06-16 8:21 ` Oliver Neukum
2013-06-16 10:35 ` Jussi Kivilinna
2013-06-28 12:39 ` Jussi Kivilinna
2013-06-28 12:58 ` Oliver Neukum
2013-06-15 13:47 ` Ming Lei
2013-06-16 10:34 ` Jussi Kivilinna
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