On 19/04/17 11:10, Arnd Bergmann wrote: > On Fri, Mar 10, 2017 at 10:23 AM, Vladimir Murzin > <[email protected]> wrote: >> R/M classes of cpus can have memory covered by MPU which in turn might >> configure RAM as Normal i.e. bufferable and cacheable. It breaks >> dma_alloc_coherent() and friends, since data can stuck in caches now >> or be buffered. >> >> This patch factors out DMA support for NOMMU configuration into >> separate entity which provides dedicated dma_ops. We have to handle >> there several cases: >> - configurations with MMU/MPU setup >> - configurations without MMU/MPU setup >> - special case for M-class, since caches and MPU there are optional >> >> In general we rely on default DMA area for coherent allocations or/and >> per-device memory reserves suitable for coherent DMA, so if such >> regions are set coherent allocations go from there. >> >> In case MPU/MPU was not setup we fallback to normal page allocator for >> DMA memory allocation. >> >> In case we run M-class cpus, for configuration without cache support >> (like Cortex-M3/M4) dma operations are forced to be coherent and wired >> with dma-noop (such decision is made based on cacheid global >> variable); however, if caches are detected there and no DMA coherent >> region is given (either default or per-device), dma is disallowed even >> MPU is not set - it is because M-class implement system memory map >> which defines part of address space as Normal memory. >> >> Reported-by: Alexandre Torgue <[email protected]> >> Reported-by: Andras Szemzo <[email protected]> >> Tested-by: Benjamin Gaignard <[email protected]> >> Tested-by: Andras Szemzo <[email protected]> >> Tested-by: Alexandre TORGUE <[email protected]> >> Reviewed-by: Robin Murphy <[email protected]> >> Signed-off-by: Vladimir Murzin <[email protected]> > > I thought I found a couple of problems with this, but after reading more > carefully I was wrong about all of them and I think the code is doing > exactly the right thing. I also like the way this is split out into a separate > set of dma_map_ops to simplify the normal MMU case. > > Acked-by: Arnd Bergmann <[email protected]> >
Much appreciated! Vladimir
