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DateWed, 2 Jan 2002 10:31:14 +0100
FromJens Axboe <>
SubjectRe: [linux-usb-devel] Re: highmem and usb [was: "sr: unaligned transfer" in 2.5.2-pre1]
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On Tue, Jan 01 2002, David Brownell wrote:
No, you can always ask to get pages low mem bounced. Highmem is no requirement, and if your device really can't support it there's no point in attempting to support it.

I presume there is some overhead in bouncing to lowmem? I imagine that highmem support for the HCDs wouldn't be that difficult -- they are just PCI devices, after all.

I'm unclear on what "bouncing to lowmem" involves, but I'd rather avoid teaching all three HCDs a second model for addressing transfer buffers.
At least until later in the 2.5 series, when we believe they'll share a lot more common code and so that new model can be taught to just ONE piece of code. Fixing bugs in one place easier than in three!

Ehm I was discussing 2.5, 2.4 will always bounce the high mem pages for you so it's moot there.

-- 
Jens Axboe

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