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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Message-ID: <6777683.xBFsv58ruI@linux-5eaq.site>
Date:	Sun, 16 Jun 2013 10:21:29 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Jussi Kivilinna <jussi.kivilinna@....fi>
Cc:	Ming Lei <tom.leiming@...il.com>, 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

On Saturday 15 June 2013 16:22:30 Jussi Kivilinna wrote:

> Hm.. rethink this a bit.
> 
> Transfer buffer might be dma aligned but shorter than cacheline and end of cacheline
> used as something else. Manual alignment by host driver does not catch that
> or fix that.
> So, yes.. dma mapping should work with unaligned buffers, but maybe the actual
> problem is multiple buffers from same cacheline.

The buffers kmalloc() returns are OK in that regard. A driver that uses
a buffer for anything but buffering is buggy.

	Regards
		Oliver

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