On Mon, Nov 03, 2014 at 06:35:28PM +0800, Herbert Xu wrote:

On Mon, Nov 03, 2014 at 10:34:46AM +0100, Maxime Ripard wrote:

quoted

What I mean is that since you are saying that drivers should do the
kmap themselves, then *all* of the drivers are broken if they are not
using it. And all of them are missing this kmap.

kmap is used by the software implementations to map the input/output
into virtual address space.  Drivers typically use DMA and operate
on physical addresses so they don't need kmap.

Yes, plus all memory allocated with GFP_KERNEL is in lowmem.

But you still haven't explain why the driver, while it doesn't handle
the user space buffer at any time, should be worried that the data the
framework has given him are actually mapped.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com