Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO

Anthony Liguori
2008-12-13T22:47:13Z

Anthony Liguori wrote:
>
> This could correspond to a:
>
> void *cpu_physical_memory_map(target_phys_addr_t addr, ram_addr_t
> size, int is_write);
>
> void cpu_physical_memory_unmap(target_physical_addr_t addr, ram_addr_t
> size, void *mapping, int is_dirty);

A really nice touch here, and note this is optional and can be a follow
up series later, would be to use the mapping itself to encode the
physical address and size so the signatures were:

void *cpu_physical_memory_map(target_phys_addr_t addr, ram_addr_t size,
int flags);
void cpu_physical_memory_unmap(void *mapping);

flags could be PHYS_MAP_READ and/or PHYS_MAP_WRITE.

In unmap, you could check to see if the address is in phys_ram_base ...
phys_ram_size. If so, you can get the physical address.

If you maintained a list of mappings, you could then search the list of
mappings based on the physical address and check the flags to see if a
flush was required.

If you also stored the address in the list, you could search on unmap if
the address was not in phys_ram_base .. phys_ram_size (which implies a
bounce buffer).

Another potential optimization would be to provide a mechanism to
explicitly set the dirty range of a physical mapping. For instance:

cpu_physical_memory_map_set_dirty(void *start, ram_addr_t size);

That would let you only copy the data that actually needed to. I think
we can probably ignore this later optimization for a while though.

Regards,

Anthony Liguori

> The whole dma.c thing should not exist. If we're going to introduce a
> higher level API, it should be a PCI DMA API.
>
> Something like virtio could use this API directly seeing as it doesn't
> really live on a PCI bus in real life.
>
> Regards,
>
> Anthony Liguori
>