On Sun, Mar 04, 2012 at 08:30:00PM -0700, Alex Williamson wrote:
On Sun, 2012-03-04 at 20:53 +0200, Michael S. Tsirkin wrote:
On Fri, Feb 24, 2012 at 04:21:17PM -0700, Alex Williamson wrote:
When a Status method is provided on a slot, the OSPM evaluates _STA in response to the device check notify on the slot. This allows some degree of a handshake between the platform and the OSPM that the hotplug has been acknowledged.
In order to implement _STA, we need to know which slots have devices. A slot with device returns 0x0F, a slot without a device returns Zero. We get this information from Qemu using the 0xae08 I/O port register. This was previously the read-side of the register written to commit a device eject and always returned 0 on read. It now returns a bitmap of present slots, so we know that reading 0 means we have and old Qemu and dynamically modify our SSDT to rename the _STA methods. This is necessary to allow backwards compatibility.
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The _STA method also writes the slot identifier to I/O port register 0xae00 as an acknowledgment of the hotplug request.
To summarize my previous messages, my notes are - not clear that we want to implement _STA: yes we can tell hypervisor what did _STA report to OSPM but this won't be needed without _STA - assuming we do, it seems clear that we want hypervisor to know what it is that we told OSPM about slot status - the specific interface used for the above is fairly tricky so it needs documentation explaining how both sides cooperate