Re: [Qemu-devel] [RFC] Memory API

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-05-19 18:28, Gleb Natapov wrote:
> On Thu, May 19, 2011 at 06:25:14PM +0200, Jan Kiszka wrote:
>> On 2011-05-19 18:17, Gleb Natapov wrote:
>>> On Thu, May 19, 2011 at 05:40:50PM +0300, Avi Kivity wrote:
>>>> On 05/19/2011 05:37 PM, Anthony Liguori wrote:
>>>>>
>>>>> So....  do you do:
>>>>>
>>>>> isa_register_region(ISABus *bus, MemoryRegion *mr, int priority)
>>>>> {
>>>>>    chipset_register_region(bus->chipset, mr, priority + 1);
>>>>> }
>>>>>
>>>>> I don't really understand how you can fold everything into one
>>>>> table and not allow devices to override their parents using
>>>>> priorities.
>>>>
>>>> Think of how a window manager folds windows with priorities onto a
>>>> flat framebuffer.
>>>>
>>>> You do a depth-first walk of the tree.  For each child list, you
>>>> iterate it from the lowest to highest priority, allowing later
>>>> subregions override earlier subregions.
>>>>
>>> And how you set those priorities in a sensible way? Why two device on a
>>> PCI bus will want to register their memory region with anything but
>>> highest priority? And if you let PCI subsystem to assign priorities how
>>> it will coordinate with ISA subsystem/memory controller what priorities
>>> to assign to get meaningful system?
>>
>> Priorities >default will only be used for explicit overlays, e.g. RAM
>> over MMIO in PAM regions. Non-default priorities won't be assigned to
>> normal PCI bars or any other device's region.
>>
> That does not explain who and how assign those priorities in globally
> meaningful way.

There are no global priorities. Priorities are only used inside each
level of the memory region hierarchy to generate a resulting, flattened
view for the next higher level. At that level, everything imported from
below has the default prio again, ie. the lowest one.

Jan

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