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Date: Sat, 25 Apr 2015 07:59:50 +0200
From: Hans Petter Selasky <hps@selasky.org>
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To: Ian Lepore <ian@freebsd.org>, Svatopluk Kraus <onwahe@gmail.com>
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Subject: Re: [patch] fix add_bounce_page() for BUS_DMA_KEEP_PG_OFFSET
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On 04/24/15 15:29, Ian Lepore wrote:
> On Fri, 2015-04-24 at 13:34 +0200, Svatopluk Kraus wrote:
>> The add_bounce_page() can be called from _bus_dmamap_load_phys().
>> Client virtual address is zero (not valid) in that case. So, client
>> physical address must be used to get an offset when
>> BUS_DMA_KEEP_PG_OFFSET flag is set. Note that client physical address
>> is always valid.
>>
>> Svatopluk Kraus
>
> The only user of BUS_DMA_KEEP_PG_OFFSET in the system is USB.  If the
> flag didn't exist, we could do bouncing with a whole lot more
> efficiency, at least in the ARM world.  I wonder if it would be possible
> to just eliminate the flag (and of course, USB's need for it, which I
> fully admit I don't understand even a little bit).
>

Hi,

USB (EHCI/UHCI/OHCI) needs this flag when computing scatter/gather 
lists. Please ensure it works like expected. The good news is XHCI needs 
it less than the EHCI.

Ian: The patch looks good - will you commit it?

--HPS