dma-mapping: replace custom code with generic implementation
Now that all of these have consistent behavior, replace them with
a single shared implementation of arch_sync_dma_for_device() and
arch_sync_dma_for_cpu() and three parameters to pick how they should
operate:
- If the CPU has speculative prefetching, then the cache
has to be invalidated after a transfer from the device.
On the rarer CPUs without prefetching, this can be skipped,
with all cache management happening before the transfer.
This flag can be runtime detected, but is usually fixed
per architecture.
- Some architectures currently clean the caches before DMA
from a device, while others invalidate it. There has not
been a conclusion regarding whether we should change all
architectures to use clean instead, so this adds an
architecture specific flag that we can change later on.
- On 32-bit Arm, the arch_sync_dma_for_cpu() function keeps
track pages that are marked clean in the page cache, to
avoid flushing them again. The implementation for this is
generic enough to work on all architectures that use the
PG_dcache_clean page flag, but a Kconfig symbol is used
to only enable it on Arm to preserve the existing behavior.
For the function naming, I picked 'wback' over 'clean', and 'wback_inv'
over 'flush', to avoid any ambiguity of what the helper functions are
supposed to do.
Moving the global functions into a header file is usually a bad idea
as it prevents the header from being included more than once, but it
helps keep the behavior as close as possible to the previous state,
including the possibility of inlining most of it into these functions
where that was done before. This also helps keep the global namespace
clean, by hiding the new arch_dma_cache{_wback,_inv,_wback_inv} from
device drivers that might use them incorrectly.
It would be possible to do this one architecture at a time, but
as the change is the same everywhere, the combined patch helps
explain it better once.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
19 files changed
