coresight: etm4x: Add support to skip trace unit power up

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 the trace unit
power up ETM register is set (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
skip powering up of trace unit after checking for this errata
via new property called "qcom,skip-power-up".
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>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200716175746.3338735-4-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm4x.c

@@ -196,12 +196,14 @@ 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);
 
+	if (!drvdata->skip_power_up) {
 		/*
 		 * Request to keep the trace unit powered and also
 		 * emulation of powerdown
 		 */
-	writel_relaxed(readl_relaxed(drvdata->base + TRCPDCR) | TRCPDCR_PU,
-		       drvdata->base + TRCPDCR);
+		writel_relaxed(readl_relaxed(drvdata->base + TRCPDCR) |
+			       TRCPDCR_PU, drvdata->base + TRCPDCR);
+	}
 
 	/* Enable the trace unit */
 	writel_relaxed(1, drvdata->base + TRCPRGCTLR);
@@ -476,10 +478,12 @@ static void etm4_disable_hw(void *info)
 
 	CS_UNLOCK(drvdata->base);
 
+	if (!drvdata->skip_power_up) {
 		/* 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);
 
@@ -1468,6 +1472,9 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 			return -ENOMEM;
 	}
 
+	if (fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
+		drvdata->skip_power_up = true;
+
 	/* Validity for the resource is already checked by the AMBA core */
 	base = devm_ioremap_resource(dev, res);
 	if (IS_ERR(base))

drivers/hwtracing/coresight/coresight-etm4x.h

@@ -407,6 +407,8 @@ struct etmv4_save_state {
  * @config:	structure holding configuration parameters.
  * @save_state:	State to be preserved across power loss
  * @state_needs_restore: True when there is context to restore after PM exit
+ * @skip_power_up: Indicates if an implementation can skip powering up
+ *		   the trace unit.
  */
 struct etmv4_drvdata {
 	void __iomem			*base;
@@ -454,6 +456,7 @@ struct etmv4_drvdata {
 	struct etmv4_config		config;
 	struct etmv4_save_state		*save_state;
 	bool				state_needs_restore;
+	bool				skip_power_up;
 };
 
 /* Address comparator access types */