On Thu, 19 Jan 2012, Matt Thomas wrote:
> For prefetchable regions (like framebuffers) mapped by bus_space_map, there
> is a need to able force the contents out of the cache back into memory
> (especially when the cache is a writeback cache).
>
> There is no MI way to do this with the bus_space framework so I'm proposing
> we add a:
>
> void bus_space_sync(bus_space_tag_t bst,
> bus_space_handle_t bsh,
> bus_size_t offset,
> bus_size_t length,
> int ops);
>
> where ops is one of:
>
> #define BUS_SPACE_SYNC_WB 1 // defined by MD
> #define BUS_SPACE_SYNC_WBINV 2 // defined by MD
>
> One caveat is that though a BUS_SPACE_SYNC_WB was requested, a platform can
> perform BUS_SPACE_SYNC_WBINV instead. If the platform can't support just
> writeback, it is allowed to silently do a writeback-invalidate instead.
Could elaborate a bit more on how you plan to use this and why
bus_space_barrier() with BUS_SPACE_BARRIER_SYNC is insufficient?
Yes, I know the current implementation ov bus_space_barrier() on the
architecture you're using doesn't do this, but why can't it be enhanced to
if you do the initial mapping with BUS_SPACE_MAP_CACHEABLE? Presumably if
bus_space_sync() is passd a handle, offset, and length you're using the
bus_space_{read,write}*() accessors rather than the pointer returned by
bus_space_vaddr().
Also, how would this work if your machine has an I/O cache (separate from
the CPU cache)?
Eduardo
