[PATCH] coresight: tmc: Enable SG capability on ACPI based SoC-400 TMC ETR devices

[Anshuman Khandual <anshuman.khandual@arm.com>]

This detects and enables the scatter gather capability (SG) on ACPI based
Soc-400 TMC ETR devices via a new property called 'arm-armhc97c-sg-enable'.
The updated ACPI spec can be found below, which contains this new property.

https://developer.arm.com/documentation/den0067/latest/

This preserves current handling for the property 'arm,scatter-gather' both
on ACPI and DT based platforms i.e the presence of the property is checked
instead of the value.

Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: coresight@lists.linaro.org 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 .../hwtracing/coresight/coresight-tmc-core.c  | 28 ++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
index 72005b0c633e..2b277499b59a 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-core.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
@@ -4,6 +4,7 @@
  * Description: CoreSight Trace Memory Controller driver
  */
 
+#include <linux/acpi.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/types.h>
@@ -360,7 +361,32 @@ static const struct attribute_group *coresight_etr_groups[] = {
 
 static inline bool tmc_etr_can_use_sg(struct device *dev)
 {
-	return fwnode_property_present(dev->fwnode, "arm,scatter-gather");
+	int ret;
+	u8 val_u8;
+
+	/*
+	 * Presence of the property 'arm,scatter-gather' is checked
+	 * on the platform for the feature support, rather than its
+	 * value.
+	 */
+	if (is_of_node(dev->fwnode)) {
+		return fwnode_property_present(dev->fwnode, "arm,scatter-gather");
+	} else if (is_acpi_device_node(dev->fwnode)) {
+		/*
+		 * TMC_DEVID_NOSCAT test in tmc_etr_setup_caps(), has already ensured
+		 * this property is only checked for Coresight SoC 400 TMC configured
+		 * as ETR.
+		 */
+		ret = fwnode_property_read_u8(dev->fwnode, "arm-armhc97c-sg-enable", &val_u8);
+		if (!ret)
+			return !!val_u8;
+
+		if (fwnode_property_present(dev->fwnode, "arm,scatter-gather")) {
+			pr_warn_once("Deprecated ACPI property - arm,scatter-gather\n");
+			return true;
+		}
+	}
+	return false;
 }
 
 static inline bool tmc_etr_has_non_secure_access(struct tmc_drvdata *drvdata)
-- 
2.25.1


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