[U-Boot] Help with exporting memory power management info in u-boot

[Ankita Garg]

Hi,

Memory hardware today offers capabilities for managing power
consumption, like multiple lower power statest. Few SoCs, like the TI
Panda board, offers support for Partial Array Self Refresh (PASR), by
which partial areas of memory could be turned off to save power.
Further, few other SoCs have multiple memory controllers, like Samsung
Exynos 4210, where each controller independently transitions memory
under it into lower power states depending on certain criteria. Each of
these capabilities are supported by the hardware at a particular
granularity. For example, PASR could be supported at the level of a
memory bank, i.e, a bank of memory that is free could be turned off,
independent of the other banks.

Inorder to exploit these features, the Linux VM subsystem needs to be
modified to take into account the physical memory topology when managing
memory. We proposed a generic memory regions infrastructure, that could
be used to tag boundaries of memory blocks which belong to a specific
memory power management domain and further enable exploitation of
platform capabilities. The details of this framework can be found here:

https://lkml.org/lkml/2011/5/27/177

Memory region is a layer of abstraction that would be created at boot
time, with information from firmware regarding the granularity at which
memory power can be managed on the platform. We would like to work
towards having this information exported by u-boot. A sample interface
we are looking at is a device tree node that would provide the number,
size and starting address corresponding to the memory power domains on
the underlying platform.

In this regard, we want some help from the u-boot community on designing
the interfaces. Further, we would like to collaborate with all the SoCs
that have support for managing memory power on their boards, so we could
design a generic interface that can be exploited by all.

-- 
Regards,
Ankita Garg (ankita at in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India