I think it would be just simpler to disallow page zero usage period. Can you think of any case where physical page 0 is ever a valid DMA address?
At the very least, require bounce buffers.
On Tue, 10 Jan 2012, Andriy Gapon wrote:
Some hardware interfaces may reserve a special meaning for a (physical) memory address value of zero. One example is the OHCI specification where a zero value in CurrentBufferPointer doesn't mean a physical address, but has a reserved meaning. To be honest I don't have another example :) but don't preclude its existence. To deal with this peculiarity we could use a special flag/quirk that would instruct the bus dma code to never use the page zero for communication with the hardware. Here's a proof of concept patch that implements the idea: http://people.freebsd.org/~avg/usb-dma-pagezero.diff Some concerns: - not sure if BUS_DMA_NO_PAGEZERO is the best name for the flag - the patch implements the flag only for x86 at the moment - usb code uses the flag regardless of the actual controller type What do you think? -- Andriy Gapon _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
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