Re: [RFC PATCH v2 03/21][SeaBIOS] acpi-dsdt: Implement functions for memory hotplug

[Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>]

On Tue, Jul 17, 2012 at 03:23:00PM +0800, Wen Congyang wrote:
> > +        Method(MESC, 0) {
> > +            // Local5 = active memdevice bitmap
> > +            Store (MES, Local5)
> > +            // Local2 = last read byte from bitmap
> > +            Store (Zero, Local2)
> > +            // Local0 = memory device iterator
> > +            Store (Zero, Local0)
> > +            While (LLess(Local0, SizeOf(MEON))) {
> > +                // Local1 = MEON flag for this memory device
> > +                Store(DerefOf(Index(MEON, Local0)), Local1)
> > +                If (And(Local0, 0x07)) {
> > +                    // Shift down previously read bitmap byte
> > +                    ShiftRight(Local2, 1, Local2)
> > +                } Else {
> > +                    // Read next byte from memdevice bitmap
> > +                    Store(DerefOf(Index(Local5, ShiftRight(Local0, 3))), Local2)
> > +                }
> > +                // Local3 = active state for this memory device
> > +                Store(And(Local2, 1), Local3)
> > +
> > +                If (LNotEqual(Local1, Local3)) {
> 
> There are two ways to hot remove a memory device:
> 1. dimm_del
> 2. echo 1 >/sys/bus/acpi/devices/PNP0C80:XX/eject
> 
> In the 2nd case, we cannot hotplug this memory device again,
> because both Local1 and Local3 are 1.
> 
> So, I think MEON flag for this meory device should be set to 0 in method _EJ0
> or implement method _PS3 for memory device.

good catch. Both internal seabios state (MEON) and the machine qemu bitmap
(mems_sts in hw/acpi_piix4.c) have to be updated when the ejection comes from
OSPM action. I will implement a _PS3 method that updates the MEON flag and also
signals qemu to change the mems_sts bitmap.

thanks,
- Vasilis