[PATCH] coresight: etm4x: Add support to disable trace unit power up

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

From: Tingwei Zhang <tingwei@codeaurora.org>

On some Qualcomm Technologies Inc. SoCs like SC7180, there
exists a hardware errata where the APSS (Application Processor
SubSystem)/CPU watchdog counter is stopped when ETM register
TRCPDCR.PU=1. Since the ETMs share the same power domain as
that of respective CPU cores, they are powered on when the
CPU core is powered on. So we can disable powering up of the
trace unit after checking for this errata via new property
called "qcom,tupwr-disable".

Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>
Co-developed-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
---
 .../devicetree/bindings/arm/coresight.txt     |  6 ++++
 drivers/hwtracing/coresight/coresight-etm4x.c | 29 ++++++++++++-------
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/Documentation/devicetree/bindings/arm/coresight.txt b/Documentation/devicetree/bindings/arm/coresight.txt
index 846f6daae71b..d2030128fe46 100644
--- a/Documentation/devicetree/bindings/arm/coresight.txt
+++ b/Documentation/devicetree/bindings/arm/coresight.txt
@@ -108,6 +108,12 @@ its hardware characteristcs.
 	* arm,cp14: must be present if the system accesses ETM/PTM management
 	  registers via co-processor 14.
 
+	* qcom,tupwr-disable: boolean. Indicates that trace unit power up can
+	  be disabled on Qualcomm Technologies Inc. systems where ETMs are in
+	  the same power domain as their CPU cores. This property is required
+	  to identify such systems with hardware errata where the CPU watchdog
+	  counter is stopped when TRCPDCR.PU=1.
+
 * Optional property for TMC:
 
 	* arm,buffer-size: size of contiguous buffer space for TMC ETR
diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
index fb0f5f4f3a91..6886b44f6947 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x.c
@@ -104,6 +104,11 @@ struct etm4_enable_arg {
 	int rc;
 };
 
+static inline bool etm4_can_disable_tupwr(struct device *dev)
+{
+	return fwnode_property_present(dev_fwnode(dev), "qcom,tupwr-disable");
+}
+
 static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
 {
 	int i, rc;
@@ -196,12 +201,14 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
 	writel_relaxed(config->vmid_mask0, drvdata->base + TRCVMIDCCTLR0);
 	writel_relaxed(config->vmid_mask1, drvdata->base + TRCVMIDCCTLR1);
 
-	/*
-	 * Request to keep the trace unit powered and also
-	 * emulation of powerdown
-	 */
-	writel_relaxed(readl_relaxed(drvdata->base + TRCPDCR) | TRCPDCR_PU,
-		       drvdata->base + TRCPDCR);
+	if (!etm4_can_disable_tupwr(etm_dev)) {
+		/*
+		 * Request to keep the trace unit powered and also
+		 * emulation of powerdown
+		 */
+		writel_relaxed(readl_relaxed(drvdata->base + TRCPDCR) | TRCPDCR_PU,
+			       drvdata->base + TRCPDCR);
+	}
 
 	/* Enable the trace unit */
 	writel_relaxed(1, drvdata->base + TRCPRGCTLR);
@@ -476,10 +483,12 @@ static void etm4_disable_hw(void *info)
 
 	CS_UNLOCK(drvdata->base);
 
-	/* power can be removed from the trace unit now */
-	control = readl_relaxed(drvdata->base + TRCPDCR);
-	control &= ~TRCPDCR_PU;
-	writel_relaxed(control, drvdata->base + TRCPDCR);
+	if (!etm4_can_disable_tupwr(etm_dev)) {
+		/* power can be removed from the trace unit now */
+		control = readl_relaxed(drvdata->base + TRCPDCR);
+		control &= ~TRCPDCR_PU;
+		writel_relaxed(control, drvdata->base + TRCPDCR);
+	}
 
 	control = readl_relaxed(drvdata->base + TRCPRGCTLR);
 
-- 
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