linux-kernel - Re: [PATCH v4 10/13] coresight: Remove misleading definitions

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Message-ID: <20251114162348.GK3568724@e132581.arm.com>
Date: Fri, 14 Nov 2025 16:23:48 +0000
From: Leo Yan <leo.yan@....com>
To: James Clark <james.clark@...aro.org>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jonathan Corbet <corbet@....net>, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 10/13] coresight: Remove misleading definitions

On Wed, Nov 12, 2025 at 03:22:16PM +0000, James Clark wrote:
> ETM_OPT_* definitions duplicate the PMU format attributes that have
> always been published in sysfs. Hardcoding them here makes it misleading
> as to what the 'real' PMU API is and prevents attributes from being
> rearranged in the future.
> 
> ETM4_CFG_BIT_* definitions just define what the Arm Architecture is
> which is not the responsibility of the kernel to do and doesn't scale to
> other registers or versions of ETM. It's not an actual software ABI/API
> and these definitions here mislead that it is.
> 
> Any tools using the first ones would be broken anyway as they won't work
> when attributes are moved, so removing them is the right thing to do and
> will prompt a fix. Tools using the second ones can trivially redefine
> them locally.
> 
> Perf also has its own copy of the headers so both of these things can be
> fixed up at a later date.
> 
> Signed-off-by: James Clark <james.clark@...aro.org>

Good cleanup for me!

Reviewed-by: Leo Yan <leo.yan@....com>

> ---
>  include/linux/coresight-pmu.h | 24 ------------------------
>  1 file changed, 24 deletions(-)
> 
> diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
> index 89b0ac0014b0..2e179abe472a 100644
> --- a/include/linux/coresight-pmu.h
> +++ b/include/linux/coresight-pmu.h
> @@ -21,30 +21,6 @@
>   */
>  #define CORESIGHT_LEGACY_CPU_TRACE_ID(cpu)  (0x10 + (cpu * 2))
>  
> -/*
> - * Below are the definition of bit offsets for perf option, and works as
> - * arbitrary values for all ETM versions.
> - *
> - * Most of them are orignally from ETMv3.5/PTM's ETMCR config, therefore,
> - * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
> - * directly use below macros as config bits.
> - */
> -#define ETM_OPT_BRANCH_BROADCAST 8
> -#define ETM_OPT_CYCACC		12
> -#define ETM_OPT_CTXTID		14
> -#define ETM_OPT_CTXTID2		15
> -#define ETM_OPT_TS		28
> -#define ETM_OPT_RETSTK		29
> -
> -/* ETMv4 CONFIGR programming bits for the ETM OPTs */
> -#define ETM4_CFG_BIT_BB         3
> -#define ETM4_CFG_BIT_CYCACC	4
> -#define ETM4_CFG_BIT_CTXTID	6
> -#define ETM4_CFG_BIT_VMID	7
> -#define ETM4_CFG_BIT_TS		11
> -#define ETM4_CFG_BIT_RETSTK	12
> -#define ETM4_CFG_BIT_VMID_OPT	15
> -
>  /*
>   * Interpretation of the PERF_RECORD_AUX_OUTPUT_HW_ID payload.
>   * Used to associate a CPU with the CoreSight Trace ID.
> 
> -- 
> 2.34.1
>