netdev - Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped

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Date:	Sat, 15 Jun 2013 15:41:04 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Jussi Kivilinna <jussi.kivilinna@....fi>
Cc:	linux-usb@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA
 aligned and are about to be DMA mapped

Cc: netdev

On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna <jussi.kivilinna@....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.

> 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.

>
> 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.

Thanks,
-- 
Ming Lei
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