coresight: etm4x: Skip accessing TRCPDCR in save/restore

When the ETM is affected by Qualcomm errata, modifying the
TRCPDCR could cause the system hang. Even though this is
taken care of during enable/disable ETM, the ETM state
save/restore could still access the TRCPDCR. Make sure
we skip the access during the save/restore.

Found by code inspection.

Link: https://lore.kernel.org/r/20210110224850.1880240-3-suzuki.poulose@arm.com
Fixes: 02510a5a ("coresight: etm4x: Add support to skip trace unit power up")
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc: Tingwei Zhang <tingwei@codeaurora.org>
Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Reviewed-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210201181351.1475223-5-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -1373,7 +1373,8 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
 
 	state->trcclaimset = readl(drvdata->base + TRCCLAIMCLR);
 
-	state->trcpdcr = readl(drvdata->base + TRCPDCR);
+	if (!drvdata->skip_power_up)
+		state->trcpdcr = readl(drvdata->base + TRCPDCR);
 
 	/* wait for TRCSTATR.IDLE to go up */
 	if (coresight_timeout(drvdata->base, TRCSTATR, TRCSTATR_IDLE_BIT, 1)) {
@@ -1391,9 +1392,9 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
 	 * potentially save power on systems that respect the TRCPDCR_PU
 	 * despite requesting software to save/restore state.
 	 */
-	writel_relaxed((state->trcpdcr & ~TRCPDCR_PU),
-			drvdata->base + TRCPDCR);
-
+	if (!drvdata->skip_power_up)
+		writel_relaxed((state->trcpdcr & ~TRCPDCR_PU),
+				drvdata->base + TRCPDCR);
 out:
 	CS_LOCK(drvdata->base);
 	return ret;
@@ -1488,7 +1489,8 @@ static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
 
 	writel_relaxed(state->trcclaimset, drvdata->base + TRCCLAIMSET);
 
-	writel_relaxed(state->trcpdcr, drvdata->base + TRCPDCR);
+	if (!drvdata->skip_power_up)
+		writel_relaxed(state->trcpdcr, drvdata->base + TRCPDCR);
 
 	drvdata->state_needs_restore = false;