On Thu, Apr 03, 2025 at 12:18:56PM +0530, Anshuman Khandual wrote:
On 3/27/25 17:07, Leo Yan wrote:
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") Signed-off-by: Leo Yan leo.yan@arm.com
include/linux/coresight.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/include/linux/coresight.h b/include/linux/coresight.h index b888f6ed59b2..26eb4a61b992 100644 --- a/include/linux/coresight.h +++ b/include/linux/coresight.h @@ -476,15 +476,18 @@ static inline bool is_coresight_device(void __iomem *base)
- Returns:
- clk - Clock is found and enabled
*/
- NULL - Clock is not needed as it is managed by the AMBA bus driver
- 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;
- pclk = devm_clk_get_enabled(dev, "apb_pclk");
- if (IS_ERR(pclk))
pclk = devm_clk_get_enabled(dev, "apb");
- if (!dev_is_amba(dev)) {
pclk = devm_clk_get_enabled(dev, "apb_pclk");if (IS_ERR(pclk))pclk = devm_clk_get_enabled(dev, "apb");- }
return pclk; }
coresight_get_enable_apb_pclk() mostly gets called in the platform driver probe paths but they are also present in some AMBA probe paths. Hence why cannot the callers in AMBA probe paths get fixed instead ?
With this approach, clocking operations are different in static probe and dynamic probe. This causes complexity for CoreSight drivers.
After consideration, we decided to use a central place for clock initialization. Patch 09 follows the idea to encapsulate pclk and atclk operations in the coresight_get_enable_clocks() function.
Besides return value never gets checked for NULL, which would have to be changed as well if coresight_get_enable_apb_pclk() starts returning NULL values for AMBA devices.
drvdata->pclk = coresight_get_enable_apb_pclk(&pdev->dev); if (IS_ERR(drvdata->pclk)) return -ENODEV;
I confirmed CoreSight drivers have used this condition, so it is safe to return NULL pointer from coresight_get_enable_apb_pclk().
Thanks, Leo