Messages in this thread | | | Date | Fri, 7 Nov 2003 10:48:43 -0500 (EST) | From | Alan Stern <> | Subject | Re: [Bug 1412] Copy from USB1 CF/SM reader stalls, no actual content is read (only directory structure) |
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On Fri, 7 Nov 2003, Jens Axboe wrote:
> I've lost the original mail in the thread, but I'm quite sure it listed > sg[0].page as being valid. Maybe the driver cleared it somewhere too > early? page_address() will not have returned NULL for a valid page. > Unless it's a highmem page, in that case you have to map it and unmap > after use. For drivers like this that aren't performance critical and > are by no means highmem ready, it's easier just to set your dma mask low > enough that you wont be handed such pages.
I think you may have put your finger on the problem. Our difficulty is that we have no control over where these sg pages are allocated; that depends on the capabilities of the USB host controller that our device happens to be plugged into. Probably all the spots in the usb-storage driver that directly access those sg pages will have to be rewritten to take into account that they may not be located in mapped memory.
So I will need to learn the proper way of doing that. Is it as simple as calling page_address(), and if the result is 0 then calling kmap() followed by kunmap()?
Alan Stern
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