Re: [PATCH v2 6/9] coresight: Avoid enable programming clock duplicately

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

On 4/23/25 20:47, 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.

Are you sure AMBA bus driver always enables such clocks in all scenarios ?
Even if that is true - why cannot coresight_get_enable_apb_pclk() ensured
to be called only for the platform drivers cases via code re-organization,
rather than changing the coresight_get_enable_apb_pclk() helper itself.

> 
> 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;
>  }