On Thu, Feb 14, 2013 at 3:09 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Thu, Feb 14, 2013 at 12:56:02PM +0000, Peter Maydell wrote: >> On 14 February 2013 12:45, Michael S. Tsirkin <m...@redhat.com> wrote: >> > overlap flag in the region is currently unused, most devices have no >> > idea whether their region overlaps with anything, so drop it, >> > assume that all regions can overlap and always require priority. >> >> Devices themselves shouldn't care, for the most part -- they just >> provide a memory region and it's their parent that has to map it >> and know whether it overlaps or not. Similarly, parents should >> generally be in control of the container they're mapping the >> memory region into, and know whether it will be an overlapping >> map or not. >> >> > It's also not clear how should devices allocate priorities. >> >> Up to the parent which controls the region being mapped into. > > We could just assume same priority as parent but what happens if it > has to be different?
Priority is only considered relative to siblings. The parent's priority is only considered wrt the parent's siblings, not its children. > There are also aliases so a region > can have multiple parents. Presumably it will have to have > different priorities depending on what the parent does? The alias region has its own priority > Here's a list of instances using priority != 0. > > hw/armv7m_nvic.c: MEMORY_PRIO_LOW); > hw/cirrus_vga.c: MEMORY_PRIO_LOW); > hw/cirrus_vga.c: MEMORY_PRIO_LOW); > hw/cirrus_vga.c: &s->low_mem_container, > MEMORY_PRIO_LOW); > hw/kvm/pci-assign.c: &r_dev->mmio, MEMORY_PRIO_LOW); > hw/kvmvapic.c: memory_region_add_subregion(as, rom_paddr, &s->rom, > MEMORY_PRIO_HIGH); > hw/lpc_ich9.c: MEMORY_PRIO_LOW); > hw/onenand.c: &s->mapped_ram, MEMORY_PRIO_LOW); > hw/pam.c: MEMORY_PRIO_LOW); > hw/pc.c: MEMORY_PRIO_LOW); > hw/pc_sysfw.c: isa_bios, MEMORY_PRIO_LOW); > hw/pc_sysfw.c: isa_bios, MEMORY_PRIO_LOW); > hw/pci/pci.c: MEMORY_PRIO_LOW); > hw/pci/pci_bridge.c: memory_region_add_subregion(parent_space, base, > alias, MEMORY_PRIO_LOW); > hw/piix_pci.c: MEMORY_PRIO_LOW); > hw/piix_pci.c: &d->rcr_mem, MEMORY_PRIO_LOW); > hw/q35.c: &mch->smram_region, MEMORY_PRIO_LOW); > hw/vga-isa.c: MEMORY_PRIO_LOW); > hw/vga.c: MEMORY_PRIO_MEDIUM); > hw/vga.c: vga_io_memory, MEMORY_PRIO_LOW); > hw/xen_pt_msi.c: MEMORY_PRIO_MEDIUM); /* > Priority: pci default + 1 > > Making priority relative to parent but not the same just seems like a recipe > for disaster. > >> I definitely don't like making the priority argument mandatory: >> this is just introducing pointless boilerplate for the common >> case where nothing overlaps and you know nothing overlaps. > > Non overlapping is not a common case at all. E.g. with normal PCI > devices you have no way to know nothing overlaps - addresses are guest > programmable. Non overlapping is mostly useful for embedded platforms.
