ARM: tegra: dvfs: Optimize Tegra3 VDD_CPU control in LP mode

Optimized Tegra3 VDD_CPU control when VDD_CPU target is set to zero,
which could happen only while CPU is in LP mode (and CPU regulator
output is turned off by side-band signal, anyway):

- Ignore VDD_CPU dependency on VDD_CORE while VDD_CPU target is zero
- Allow VDD_CPU one step change to zero (i.e., to minimum voltage set
by constraints) after entry to LP mode
- Allow VDD_CPU one step change to the predicted G mode target before
exit from LP mode

(cherry picked from commit 5826f3e28867207b5dad1c50795de8275d1af872)
(cherry picked from commit 79c531421dfc65e27af657fd12b64c4187c67827)

Change-Id: I3c469132034a431d2e9b8727d11d604c306122f1
Reviewed-on: http://git-master/r/63357
Reviewed-by: Varun Colbert <vcolbert@nvidia.com>
Tested-by: Varun Colbert <vcolbert@nvidia.com>

Rebase-Id: R4c4f6e79decddb778f58cb5eef853a4c9d52ca94

3 files changed, 15 insertions, 3 deletions

diff --git a/arch/arm/mach-tegra/dvfs.c b/arch/arm/mach-tegra/dvfs.c
index dc0d779870a6..2276c8befbe5 100644
--- a/arch/arm/mach-tegra/dvfs.c
+++ b/arch/arm/mach-tegra/dvfs.c
@@ -98,6 +98,7 @@ static int dvfs_rail_set_voltage(struct dvfs_rail *rail, int millivolts)
 	int step = (millivolts > rail->millivolts) ? rail->step : -rail->step;
 	int i;
 	int steps;
+	bool jmp_to_zero;
 
 	if (!rail->reg) {
 		if (millivolts == rail->millivolts)
@@ -110,10 +111,14 @@ static int dvfs_rail_set_voltage(struct dvfs_rail *rail, int millivolts)
 		return 0;
 
 	rail->resolving_to = true;
-	steps = DIV_ROUND_UP(abs(millivolts - rail->millivolts), rail->step);
+	jmp_to_zero = rail->jmp_to_zero &&
+			((millivolts == 0) || (rail->millivolts == 0));
+	steps = jmp_to_zero ? 1 :
+		DIV_ROUND_UP(abs(millivolts - rail->millivolts), rail->step);
 
 	for (i = 0; i < steps; i++) {
-		if (abs(millivolts - rail->millivolts) > rail->step)
+		if (!jmp_to_zero &&
+		    (abs(millivolts - rail->millivolts) > rail->step))
 			rail->new_millivolts = rail->millivolts + step;
 		else
 			rail->new_millivolts = millivolts;
diff --git a/arch/arm/mach-tegra/dvfs.h b/arch/arm/mach-tegra/dvfs.h
index d867ac4299cf..60f8d51c6f1a 100644
--- a/arch/arm/mach-tegra/dvfs.h
+++ b/arch/arm/mach-tegra/dvfs.h
@@ -49,6 +49,7 @@ struct dvfs_rail {
 	int max_millivolts;
 	int nominal_millivolts;
 	int step;
+	bool jmp_to_zero;
 	bool disabled;
 	bool updating;
 	bool resolving_to;
diff --git a/arch/arm/mach-tegra/tegra3_dvfs.c b/arch/arm/mach-tegra/tegra3_dvfs.c
index 1acc76a3eda3..2f1e28815dcb 100644
--- a/arch/arm/mach-tegra/tegra3_dvfs.c
+++ b/arch/arm/mach-tegra/tegra3_dvfs.c
@@ -60,6 +60,7 @@ static struct dvfs_rail tegra3_dvfs_rail_vdd_cpu = {
 	.max_millivolts = 1250,
 	.min_millivolts = 850,
 	.step = VDD_SAFE_STEP,
+	.jmp_to_zero = true,
 };
 
 static struct dvfs_rail tegra3_dvfs_rail_vdd_core = {
@@ -102,7 +103,12 @@ static int tegra3_dvfs_rel_vdd_cpu_vdd_core(struct dvfs_rail *vdd_cpu,
 static int tegra3_dvfs_rel_vdd_core_vdd_cpu(struct dvfs_rail *vdd_core,
 	struct dvfs_rail *vdd_cpu)
 {
-	int cpu_floor = max(vdd_core->new_millivolts, vdd_core->millivolts) -
+	int cpu_floor;
+
+	if (vdd_cpu->new_millivolts == 0)
+		return 0; /* If G CPU is off, core relations can be ignored */
+
+	cpu_floor = max(vdd_core->new_millivolts, vdd_core->millivolts) -
 		cpu_below_core;
 	return max(vdd_cpu->new_millivolts, cpu_floor);
 }