On 04/25/15 07:59, Hans Petter Selasky wrote:
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).


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?

The reason is that the EHCI/UHCI/OHCI doesn't have separate length fields for each data chunk and somtimes use the "0x1000 - (addr & 0xFFF)" formula to compute how many bytes are left of a transfer when a transfer wraps around 0x1000. Thank you for you understanding this is not a USB problem in general.


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