linux-kernel - Re: [PATCH] coresight: etm4x: Remove redundant claim register setting

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Message-ID: <16bf2a1e-2a98-41b3-b780-c0215db5a6dc@linaro.org>
Date: Thu, 1 May 2025 11:54:58 +0100
From: James Clark <james.clark@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
 Mike Leach <mike.leach@...aro.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: etm4x: Remove redundant claim register setting



On 01/05/2025 11:42 am, Leo Yan wrote:
> The claim register is set twice in the restore flow; remove the
> duplicate operation.
> 
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 5c20ed4cf4ed..228317991ec2 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1958,8 +1958,6 @@ static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata)
>   	if (drvdata->numvmidc > 4)
>   		etm4x_relaxed_write32(csa, state->trcvmidcctlr0, TRCVMIDCCTLR1);
>   
> -	etm4x_relaxed_write32(csa, state->trcclaimset, TRCCLAIMSET);
> -
>   	if (!drvdata->skip_power_up)
>   		etm4x_relaxed_write32(csa, state->trcpdcr, TRCPDCR);
>   

Reviewed-by: James Clark <james.clark@...aro.org>

Semi-related to this patch but probably not worth fixing: There's 
technically a race condition with an external debugger here. It would be 
better to use coresight_claim_device_unlocked() and report the error 
that's returned instead of manually writing to the whole claim register 
without checking it before and after like the claim function does.