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regulator: Introduce TI Adaptive Body Bias(ABB) on-chip LDO driver
Adaptive Body Biasing (ABB) modulates transistor bias voltages dynamically in order to optimize switching speed versus leakage. Texas Instruments' SmartReflex 2 technology provides support for this power management technique with Forward Body Biasing (FBB) and Reverse Body Biasing (RBB). These modulate the body voltage of transistor cells or blocks dynamically to gain performance and reduce leakage. TI's SmartReflex white paper[1] has further information for usage in conjunction with other power management techniques. The application of FBB/RBB technique is determined for each unique device in some process nodes, whereas, they are mandated on other process nodes. In a nutshell, ABB technique is implemented on TI SoC as an on-chip LDO which has ABB module controlling the bias voltage. However, the voltage is unique per device. These vary per SoC family and the manner in which these techniques are used may vary depending on the Operating Performance Point (OPP) voltage targeted. For example: OMAP3630/OMAP4430: certain OPPs mandate usage of FBB independent of devices. OMAP4460/OMAP4470: certain OPPs mandate usage of FBB, while others may optionally use FBB or optimization with RBB. OMAP5: ALL OPPs may optionally use ABB, and ABB biasing voltage is influenced by vset fused in s/w and requiring s/w override of default values. Further, two generations of ABB module are used in various TI SoCs. They have remained mostly register field compatible, however the register offset had switched between versions. We introduce ABB LDO support in the form of a regulator which is controlled by voltages denoting the desired Operating Performance Point which is targeted. However, since ABB transition is part of OPP change sequence, the sequencing required to ensure sane operation w.r.t OPP change is left to the controlling driver (example: cpufreq SoC driver) using standard regulator operations. The driver supports all ABB modes and ability to override ABB LDO vset control efuse based ABB mode detection etc. Current implementation is heavily influenced by the original patch series [2][3] from Mike Turquette. However, the current implementation supports only device tree based information. [1] http://www.ti.com/pdfs/wtbu/smartreflex_whitepaper.pdf [2] http://marc.info/?l=linux-omap&m=134931341818379&w=2 [3] http://marc.info/?l=linux-arm-kernel&m=134931402406853&w=2 [nm@ti.com: co-developer] Signed-off-by:Nishanth Menon <nm@ti.com> Signed-off-by: