linux-kernel - [PATCH v2 2/2] ARM: tegra: Use WFE for power-gating on Tegra30

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Date:   Tue, 30 Jul 2019 20:23:40 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] ARM: tegra: Use WFE for power-gating on Tegra30

Turned out that WFI doesn't work reliably on Tegra30 as a trigger for
the power-gating, it causes CPU hang under some circumstances like having
memory controller running of PLLP. The TRM doc states that WFI should be
used for the Big-Little "Cluster Switch", while WFE for the power-gating.
Hence let's use the WFE for CPU0 power-gating, like it is done for the
power-gating of a secondary cores. This fixes CPU hang after entering LP2
with memory running off PLLP.

Acked-by: Peter De Schrijver <pdeschrijver@...dia.com>
Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 arch/arm/mach-tegra/sleep-tegra30.S |  4 +++-
 drivers/soc/tegra/flowctrl.c        | 19 +++++++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/arm/mach-tegra/sleep-tegra30.S b/arch/arm/mach-tegra/sleep-tegra30.S
index 6c28395d8c75..17f7a2a6a494 100644
--- a/arch/arm/mach-tegra/sleep-tegra30.S
+++ b/arch/arm/mach-tegra/sleep-tegra30.S
@@ -683,10 +683,12 @@ tegra30_enter_sleep:
 	dsb
 	ldr	r0, [r6, r2] /* memory barrier */
 
+	cmp	r10, #TEGRA30
 halted:
 	isb
 	dsb
-	wfi	/* CPU should be power gated here */
+	wfine	/* CPU should be power gated here */
+	wfeeq
 
 	/* !!!FIXME!!! Implement halt failure handler */
 	b	halted
diff --git a/drivers/soc/tegra/flowctrl.c b/drivers/soc/tegra/flowctrl.c
index b6bdeef33db1..eb96a3086d6d 100644
--- a/drivers/soc/tegra/flowctrl.c
+++ b/drivers/soc/tegra/flowctrl.c
@@ -91,8 +91,23 @@ void flowctrl_cpu_suspend_enter(unsigned int cpuid)
 		reg &= ~TEGRA30_FLOW_CTRL_CSR_WFE_BITMAP;
 		/* clear wfi bitmap */
 		reg &= ~TEGRA30_FLOW_CTRL_CSR_WFI_BITMAP;
-		/* pwr gating on wfi */
-		reg |= TEGRA30_FLOW_CTRL_CSR_WFI_CPU0 << cpuid;
+
+		if (tegra_get_chip_id() == TEGRA30) {
+			/*
+			 * The wfi doesn't work well on Tegra30 because
+			 * CPU hangs under some odd circumstances after
+			 * power-gating (like memory running off PLLP),
+			 * hence use wfe that is working perfectly fine.
+			 * Note that Tegra30 TRM doc clearly stands that
+			 * wfi should be used for the "Cluster Switching",
+			 * while wfe for the power-gating, just like it
+			 * is done on Tegra20.
+			 */
+			reg |= TEGRA20_FLOW_CTRL_CSR_WFE_CPU0 << cpuid;
+		} else {
+			/* pwr gating on wfi */
+			reg |= TEGRA30_FLOW_CTRL_CSR_WFI_CPU0 << cpuid;
+		}
 		break;
 	}
 	reg |= FLOW_CTRL_CSR_INTR_FLAG;			/* clear intr flag */
-- 
2.22.0