linux-kernel - Re: [PATCH v3 6/9] coresight: Avoid enable programming clock duplicately

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Message-ID: <b30fc361-a04f-4a48-b8e2-f7c2da213e6c@arm.com>
Date: Mon, 9 Jun 2025 17:58:34 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Leo Yan <leo.yan@....com>, Mike Leach <mike.leach@...aro.org>,
 James Clark <james.clark@...aro.org>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/9] coresight: Avoid enable programming clock
 duplicately

On 09/06/2025 17:00, 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@....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 dd2b4cc7a2b70cf060a3207548fe80e3824c489f..9afa1f76c78a3347e54d94fe9a9ebed72e3fff8e 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -480,15 +480,18 @@ 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");

AMBA driver doesn't handle "apb" clock ? So we may need to retain that 
here ?

Otherwise looks good to me.

Suzuki
> +	}
>   
>   	return pclk;
>   }
>