Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxxxxxx> --- Documentation/pasr.txt | 183 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 183 insertions(+), 0 deletions(-) create mode 100644 Documentation/pasr.txt diff --git a/Documentation/pasr.txt b/Documentation/pasr.txt new file mode 100644 index 0000000..d40e3f6 --- /dev/null +++ b/Documentation/pasr.txt @@ -0,0 +1,183 @@ +Partial Array Self-Refresh Framework + +(C) 2012 Maxime Coquelin <maxime.coquelin@xxxxxxxxxxxxxx>, ST-Ericsson. + +CONTENT +1. Introduction +2. Command-line parameters +3. Allocators patching +4. PASR platform drivers + + +1. Introduction + +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. + +Interleaving example: + + 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 1 | +_______________________________ | +| 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 | +|______________________________| + +In the above example, bank 0 of die 0 is interleaved with bank0 of die 0. +The interleaving is done in HW by inverting some addresses lines. The goal is +to improve DDR bandwidth. +Practically, one buffer seen as contiguous by the kernel might be spread +into two DDR dies physically. + + +2. Command-line parameters + +To buid the DDR physical layout representation, two parameters are requested: + +* ddr_die (mandatory): Should be added for every DDR dies present in the system. + - Usage: ddr_die=xxx[M|G]@yyy[M|G] where xxx represents the size and yyy + the base address of the die. E.g.: ddr_die=512M@0 ddr_die=512M@512M + +* interleaved (optionnal): Should be added for every interleaved dependencies. + - Usage: interleaved=xxx[M|G]@yyy[M|G]:zzz[M|G] where xxx is the size of + the interleaved area between the adresses yyy and zzz. E.g + interleaved=256M@0:512M + + +3. Allocator patching + +Any allocators might call the PASR Framework for DDR power savings. Currently, +only Linux Buddy allocator is patched, but HWMEM and PMEM physically +contiguous memory allocators will follow. + +Linux Buddy allocator porting uses Buddy specificities to reduce the overhead +induced by the PASR Framework counter updates. Indeed, the PASR Framework is +called only when MAX_ORDER (4MB page blocs by default) buddies are +inserted/removed from the free lists. + +To port PASR FW into a new allocator: + +* Call pasr_put(phys_addr, size) each time a memory chunk becomes unused. +* Call pasr_get(phys_addr, size) each time a memory chunk becomes used. + +4. PASR platform drivers + +The MR16/MR17 PASR mask registers are generally accessible through the DDR +controller. At probe time, the DDR controller driver should register the +callback used by PASR Framework to apply the refresh mask for every DDR die +using pasr_register_mask_function(die_addr, callback, cookie). + +The callback passed to apply mask must not sleep since it can me called in +interrupt contexts. + -- 1.7.8 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . 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