On Wed, 28 Mar 2007, Tony Lindgren wrote:

> Hi,
> 
> Here's a little patch to make sure tranfer_buffer is always if DMA
> is temporarily unavailable. I ran into this with tusb6010 that
> currently can only do limited DMA. This fixes a problem of connecting
> storage devices and doing mixed DMA/PIO access.

Your patch isn't correct, or at least, it is very misleading.  It calls 
page_address() in a situation where it cannot be certain that the page 
frame lies in accessible kernel memory.  On some systems the value it 
calculates will be garbage.

At a minimum you need to add a comment explaining that if the page isn't
accessible, the transfer_buffer value won't ever be used.

Alan Stern


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