I was kinda hoping for something a bit simpler than that.  I'd boil down
what you were saying to this:

     1. The kernel must be aware of how the pieces of hardware are
        mapped in to the system's physical address space
     2. The kernel must have a mechanism in place to minimize access to
        specific pieces of hardware 
     3. For destructive power-down operations, the kernel should have a
        mechanism in place to ensure that no valuable data is contained
        in the memory to be powered down.

Is that complete?

On Wed, 2011-06-29 at 18:30 +0530, Ankita Garg wrote:

1) Dynamic Power Transition: The memory controller can have the ability
to automatically transition regions of memory into lower power states
when they are devoid of references for a pre-defined threshold amount of
time. Memory contents are preserved in the low power states and accessing
memory that is at a low power state takes a latency hit.

2) Dynamic Power Off: If a region is free/unallocated, the software can
indicate to the controller to completely turn off power to a certain
region. Memory contents are lost and hence the software has to be
absolutely sure about the usage statistics of the particular region. This
is a runtime capability, where the required amount of memory can be
powered 'ON' to match the workload demands.

3) Partial Array Self-Refresh (PASR): If a certain regions of memory is
free/unallocated, the software can indicate to the controller to not
refresh that region when the system goes to suspend-to-ram state and
thereby save standby power consumption.

(3) is simply a subset of (2), but with the additional restriction that
the power off can only occur during a suspend operation.  

Let's say we fully implemented support for (2).  What would be missing
to support PASR?

-- Dave

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