ARM: OMAP5 / DRA7: PM: Enable Mercury retention mode on CPUx powerdomains

In addition to the standard power-management technique, the OMAP5 / DRA7
MPU subsystem also employs an SR3-APG (mercury) power management
technology to reduce leakage.

It allows for full logic and memories retention on MPU_C0 and MPU_C1 and
is controlled by the PRCM_MPU. Only "Fast-mode" is supported on the
OMAP5 and DRA7 family of processors.
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
[nm@ti.com: minor consolidation]
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>

arch/arm/mach-omap2/omap-mpuss-lowpower.c

@@ -320,6 +320,21 @@ int omap4_hotplug_cpu(unsigned int cpu, unsigned int power_state)
 }
 
 
+/*
+ * Enable Mercury Fast HG retention mode by default.
+ */
+static void enable_mercury_retention_mode(void)
+{
+	u32 reg;
+
+	reg = omap4_prcm_mpu_read_inst_reg(OMAP54XX_PRCM_MPU_DEVICE_INST,
+				  OMAP54XX_PRCM_MPU_PRM_PSCON_COUNT_OFFSET);
+	/* Enable HG_EN, HG_RAMPUP = fast mode */
+	reg |= BIT(24) | BIT(25);
+	omap4_prcm_mpu_write_inst_reg(reg, OMAP54XX_PRCM_MPU_DEVICE_INST,
+				      OMAP54XX_PRCM_MPU_PRM_PSCON_COUNT_OFFSET);
+}
+
 /*
  * Initialise OMAP4 MPUSS
  */
@@ -397,6 +412,7 @@ int __init omap4_mpuss_init(void)
 		cpu_context_offset = OMAP4_RM_CPU0_CPU0_CONTEXT_OFFSET;
 	} else if (soc_is_omap54xx() || soc_is_dra7xx()) {
 		cpu_context_offset = OMAP54XX_RM_CPU0_CPU0_CONTEXT_OFFSET;
+		enable_mercury_retention_mode();
 	}
 
 	return 0;