[PATCH 1/3] coresight etm4x: Early clear TRCOSLAR.OSLK prior to TRCIDR1 read

[Steve Clevenger]

Add Ampere early clear of ETM TRCOSLAR.OSLK prior to TRCIDR1 access.
Ampere Computing erratum AC03_DEBUG_06 describes an Ampere
Computing design decision MMIO reads are considered the same as an
external debug access. If TRCOSLAR.OSLK is set, the TRCIDR1 access
results in a bus fault followed by a kernel panic.  A TRCIDR1 read
is valid regardless of TRCOSLAR.OSLK provided MMIO access
(now deprecated) is supported.
AC03_DEBUG_06 is described in the AmpereOne Developer Errata:
https://solutions.amperecomputing.com/customer-connect/products/AmpereOne-device-documentation

Add Ampere ETM PID required for Coresight ETM driver support.

Signed-off-by: Steve Clevenger <scclevenger at os.amperecomputing.com>
---
 .../coresight/coresight-etm4x-core.c          | 36 +++++++++++++++----
 drivers/hwtracing/coresight/coresight-etm4x.h |  2 ++
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 1cc052979e01..533be1928a09 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1091,19 +1091,34 @@ static void etm4_init_arch_data(void *info)
 	drvdata = dev_get_drvdata(init_arg->dev);
 	csa = init_arg->csa;
 
+	/* Detect the support for OS Lock before we actually use it */
+	etm_detect_os_lock(drvdata, csa);
+
+	/*
+	 * For ETM implementations that consider MMIO an external access
+	 * clear TRCOSLAR.OSLK early.
+	 */
+	if (drvdata->mmio_external)
+		etm4_os_unlock_csa(drvdata, csa);
+
 	/*
 	 * If we are unable to detect the access mechanism,
 	 * or unable to detect the trace unit type, fail
-	 * early.
+	 * early. Reset TRCOSLAR.OSLK if cleared.
 	 */
-	if (!etm4_init_csdev_access(drvdata, csa))
+	if (!etm4_init_csdev_access(drvdata, csa)) {
+		if (drvdata->mmio_external)
+			etm4_os_lock(drvdata);
 		return;
+	}
 
-	/* Detect the support for OS Lock before we actually use it */
-	etm_detect_os_lock(drvdata, csa);
+	/*
+	 * Make sure all registers are accessible
+	 * TRCOSLAR.OSLK may already be clear
+	 */
+	if (!drvdata->mmio_external)
+		etm4_os_unlock_csa(drvdata, csa);
 
-	/* Make sure all registers are accessible */
-	etm4_os_unlock_csa(drvdata, csa);
 	etm4_cs_unlock(drvdata, csa);
 
 	etm4_check_arch_features(drvdata, init_arg->pid);
@@ -2027,6 +2042,14 @@ static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
 	init_arg.csa = &access;
 	init_arg.pid = etm_pid;
 
+	/*
+	 * Ampere ETM v4.6 considers MMIO access as external. This mask
+	 * isolates the manufacturer JEP106 ID in the PID.
+	 * TRCPIDR2 (JEDC|DES_1) << 16 | TRCPIDR1 (DES_0) << 8)
+	 */
+	if ((init_arg.pid & 0x000FF000) == 0x00096000)
+		drvdata->mmio_external = true;
+
 	/*
 	 * Serialize against CPUHP callbacks to avoid race condition
 	 * between the smp call and saving the delayed probe.
@@ -2192,6 +2215,7 @@ static const struct amba_id etm4_ids[] = {
 	CS_AMBA_ID(0x000bb95e),			/* Cortex-A57 */
 	CS_AMBA_ID(0x000bb95a),			/* Cortex-A72 */
 	CS_AMBA_ID(0x000bb959),			/* Cortex-A73 */
+	CS_AMBA_UCI_ID(0x00096000, uci_id_etm4),/* Ampere ARMv8 */
 	CS_AMBA_UCI_ID(0x000bb9da, uci_id_etm4),/* Cortex-A35 */
 	CS_AMBA_UCI_ID(0x000bbd05, uci_id_etm4),/* Cortex-A55 */
 	CS_AMBA_UCI_ID(0x000bbd0a, uci_id_etm4),/* Cortex-A75 */
diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
index 4b21bb79f168..cf4f9f2e1807 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x.h
+++ b/drivers/hwtracing/coresight/coresight-etm4x.h
@@ -1015,6 +1015,7 @@ struct etmv4_save_state {
  * @skip_power_up: Indicates if an implementation can skip powering up
  *		   the trace unit.
  * @arch_features: Bitmap of arch features of etmv4 devices.
+ * @mmio_external: True if ETM considers MMIO an external access.
  */
 struct etmv4_drvdata {
 	void __iomem			*base;
@@ -1067,6 +1068,7 @@ struct etmv4_drvdata {
 	bool				state_needs_restore;
 	bool				skip_power_up;
 	DECLARE_BITMAP(arch_features, ETM4_IMPDEF_FEATURE_MAX);
+	bool				mmio_external;
 };
 
 /* Address comparator access types */
-- 
2.25.1