linux-kernel - [PATCH v6 06/10] coresight: Avoid enable programming clock duplicately

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Message-Id: <20250731-arm_cs_fix_clock_v4-v6-6-1dfe10bb3f6f@arm.com>
Date: Thu, 31 Jul 2025 13:23:42 +0100
From: Leo Yan <leo.yan@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>, 
 Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>, 
 Anshuman Khandual <anshuman.khandual@....com>, 
 Yeoreum Yun <yeoreum.yun@....com>, 
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Mark Brown <broonie@...nel.org>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, Leo Yan <leo.yan@....com>
Subject: [PATCH v6 06/10] coresight: Avoid enable programming clock
 duplicately

The programming clock is enabled by AMBA bus driver before a dynamic
probe. As a result, a CoreSight driver may redundantly enable the same
clock.

To avoid this, add a check for device type and skip enabling the
programming clock for AMBA devices. The returned NULL pointer will be
tolerated by the drivers.

Fixes: 73d779a03a76 ("coresight: etm4x: Change etm4_platform_driver driver for MMIO devices")
Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@....com>
Tested-by: James Clark <james.clark@...aro.org>
Signed-off-by: Leo Yan <leo.yan@....com>
---
 include/linux/coresight.h | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 1e652e157841955864a4bce00b2285efcad327aa..bb49080ec8f96bb23cab2efa23eb026646a3c4f4 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -481,20 +481,23 @@ static inline bool is_coresight_device(void __iomem *base)
  * Returns:
  *
  * clk   - Clock is found and enabled
- * NULL  - Clock is controlled by firmware (ACPI device only)
+ * NULL  - Clock is controlled by firmware (ACPI device only) or when managed
+ *	   by the AMBA bus driver instead
  * ERROR - Clock is found but failed to enable
  */
 static inline struct clk *coresight_get_enable_apb_pclk(struct device *dev)
 {
-	struct clk *pclk;
+	struct clk *pclk = NULL;
 
 	/* Firmware controls clocks for an ACPI device. */
 	if (has_acpi_companion(dev))
 		return NULL;
 
-	pclk = devm_clk_get_optional_enabled(dev, "apb_pclk");
-	if (!pclk)
-		pclk = devm_clk_get_optional_enabled(dev, "apb");
+	if (!dev_is_amba(dev)) {
+		pclk = devm_clk_get_optional_enabled(dev, "apb_pclk");
+		if (!pclk)
+			pclk = devm_clk_get_optional_enabled(dev, "apb");
+	}
 
 	return pclk;
 }

-- 
2.34.1