Re: [Qemu-devel] [RFC v1] Add declarations for hierarchical memory region API

[Avi Kivity]

On 05/20/2011 08:59 PM, Blue Swirl wrote:
> On Thu, May 19, 2011 at 5:12 PM, Avi Kivity<address@hidden>  wrote:
> >  The memory API separates the attributes of a memory region (its size, how
> >  reads or writes are handled, dirty logging, and coalescing) from where it
> >  is mapped and whether it is enabled.  This allows a device to configure
> >  a memory region once, then hand it off to its parent bus to map it according
> >  to the bus configuration.
> >
> >  Hierarchical registration also allows a device to compose a region out of
> >  a number of sub-regions with different properties; for example some may be
> >  RAM while others may be MMIO.

> >  +void memory_region_set_log(MemoryRegion *mr, bool log, unsigned client);
> >  +/* Enable memory coalescing for the region.  MMIO ->write callbacks may be
> >  + * delayed until a non-coalesced MMIO is issued.
> >  + */
> >  +void memory_region_set_coalescing(MemoryRegion *mr);
> >  +/* Enable memory coalescing for a sub-range of the region.  MMIO ->write
> >  + * callbacks may be delayed until a non-coalesced MMIO is issued.
> >  + */
> >  +void memory_region_add_coalescing(MemoryRegion *mr,
> >  +                                  target_phys_addr_t offset,
> >  +                                  target_phys_addr_t size);
> >  +/* Disable MMIO coalescing for the region. */
> >  +void memory_region_clear_coalescing(MemoryRegion *mr);
>
> Perhaps the interface could be more generic, like
> +void memory_region_set_property(MemoryRegion *mr, unsigned flags);
> +void memory_region_clear_property(MemoryRegion *mr, unsigned flags);

Coalescing is a complex property, not just a boolean attribute.  We 
probably will have a number of boolean attributes later, though.

> >  + * conflicts are resolved by having a higher @priority hide a lower 
> @priority.
> >  + * Subregions without priority are taken as @priority 0.
> >  + */
> >  +void memory_region_add_subregion_overlap(MemoryRegion *mr,
> >  +                                         target_phys_addr_t offset,
> >  +                                         MemoryRegion *subregion,
> >  +                                         unsigned priority);
> >  +/* Remove a subregion. */
> >  +void memory_region_del_subregion(MemoryRegion *mr,
> >  +                                 MemoryRegion *subregion);
>
> What would the subregions be used for?

Subregions describe the flow of data through the memory bus.  We'd have 
a subregion for the PCI bus, with its own subregions for various BARs, 
with some having subregions for dispatching different MMIO types within 
the BAR.

This allows, for example, the PCI layer to move a BAR without the PCI 
device knowing anything about it.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.