PASR Frameworks brings support for the Partial Array Self-Refresh DDR power management feature. PASR has been introduced in LP-DDR2, and is also present in DDR3.
PASR provides 4 modes:
* Single-Ended: Only 1/1, 1/2, 1/4 or 1/8 are refreshed, masking starting at the end of the DDR die.
* Double-Ended: Same as Single-Ended, but refresh-masking does not start necessairly at the end of the DDR die.
* Bank-Selective: Refresh of each bank of a die can be masked or unmasked via a dedicated DDR register (MR16). This mode is convenient for DDR configured in BRC (Bank-Row-Column) mode.
* Segment-Selective: Refresh of each segment of a die can be masked or unmasked via a dedicated DDR register (MR17). This mode is convenient for DDR configured in RBC (Row-Bank-Column) mode.
The role of this framework is to stop the refresh of unused memory to enhance DDR power consumption.
It supports Bank-Selective and Segment-Selective modes, as the more adapted to modern OSes.
At early boot stage, a representation of the physical DDR layout is built:
Die 0 _______________________________ | I--------------------------I | | I Bank or Segment 0 I | | I--------------------------I | | I--------------------------I | | I Bank or Segment 1 I | | I--------------------------I | | I--------------------------I | | I Bank or Segment ... I | | I--------------------------I | | I--------------------------I | | I Bank or Segment n I | | I--------------------------I | |______________________________| ...
Die n _______________________________ | I--------------------------I | | I Bank or Segment 0 I | | I--------------------------I | | I--------------------------I | | I Bank or Segment 1 I | | I--------------------------I | | I--------------------------I | | I Bank or Segment ... I | | I--------------------------I | | I--------------------------I | | I Bank or Segment n I | | I--------------------------I | |______________________________|
The first level is a table where elements represent a die: * Base address, * Number of segments, * Table representing banks/segments, * MR16/MR17 refresh mask, * DDR Controller callback to update MR16/MR17 refresh mask.
The second level is the section tables representing the banks or segments, depending on hardware configuration: * Base address, * Unused memory size counter, * Possible pointer to another section it depends on (E.g. Interleaving)
When some memory becomes unused, the allocator owning this memory calls the PASR Framework's pasr_put(phys_addr, size) function. The framework finds the sections impacted and updates their counters accordingly. If a section counter reach the section size, the refresh of the section is masked. If the corresponding section has a dependency with another section (E.g. because of DDR interleaving, see figure below), it checks the "paired" section is also unused before updating the refresh mask.
When some unused memory is requested by the allocator, the allocator owning this memory calls the PASR Framework's pasr_get(phys_addr, size) function. The framework find the section impacted and updates their counters accordingly. If before the update, the section counter was to the section size, the refrewh of the section is unmasked. If the corresponding section has a dependency with another section, it also unmask the refresh of the other section.
Patch 3/6 contains modifications for the Buddy allocator. Overhead induced is very low because the PASR framework is notified only on "MAX_ORDER" pageblocs. Any allocator support(PMEM, HWMEM...) and Memory Hotplug would be added in next patch set revisions.
Maxime Coquelin (6): PASR: Initialize DDR layout PASR: Add core Framework PASR: mm: Integrate PASR in Buddy allocator PASR: Call PASR initialization PASR: Add Documentation PASR: Ux500: Add PASR support
Documentation/pasr.txt | 183 ++++++++++++ arch/arm/Kconfig | 1 + arch/arm/kernel/setup.c | 1 + arch/arm/mach-ux500/include/mach/hardware.h | 11 + arch/arm/mach-ux500/include/mach/memory.h | 8 + drivers/mfd/db8500-prcmu.c | 67 +++++ drivers/staging/Kconfig | 2 + drivers/staging/Makefile | 1 + drivers/staging/pasr/Kconfig | 19 ++ drivers/staging/pasr/Makefile | 6 + drivers/staging/pasr/core.c | 168 +++++++++++ drivers/staging/pasr/helper.c | 84 ++++++ drivers/staging/pasr/helper.h | 16 + drivers/staging/pasr/init.c | 403 +++++++++++++++++++++++++++ drivers/staging/pasr/ux500.c | 58 ++++ include/linux/pasr.h | 143 ++++++++++ include/linux/ux500-pasr.h | 11 + init/main.c | 8 + mm/page_alloc.c | 9 + 19 files changed, 1199 insertions(+), 0 deletions(-) create mode 100644 Documentation/pasr.txt create mode 100644 drivers/staging/pasr/Kconfig create mode 100644 drivers/staging/pasr/Makefile create mode 100644 drivers/staging/pasr/core.c create mode 100644 drivers/staging/pasr/helper.c create mode 100644 drivers/staging/pasr/helper.h create mode 100644 drivers/staging/pasr/init.c create mode 100644 drivers/staging/pasr/ux500.c create mode 100644 include/linux/pasr.h create mode 100644 include/linux/ux500-pasr.h