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Message-ID: <063577a4-1530-4658-9838-934b0606e8e0@arm.com>
Date: Fri, 2 May 2025 12:08:55 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Leo Yan <leo.yan@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 6/9] coresight: Avoid enable programming clock
duplicately
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@....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;
> }
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