linux-kernel - Re: [PATCH 04/19] coresight: trbe: Remove set_trbe

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Message-ID: <789573eb-c12b-419f-80bc-3de65367583e@arm.com>
Date: Thu, 4 Dec 2025 18:13:56 +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>,
 Yeoreum Yun <yeoreum.yun@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Tamas Petz <tamas.petz@....com>,
 Tamas Zsoldos <tamas.zsoldos@....com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 04/19] coresight: trbe: Remove set_trbe_disabled() from
 the enable flow

On 01/12/25 4:51 PM, Leo Yan wrote:
> set_trbe_disabled() should never appear in the enable flow, otherwise,
> it may potentially hide bugs in the disable flow.
> 
> Remove set_trbe_disabled() from the enable path.

IIRC without first disabling TRBLIMITR_EL1_E - TRBE registers or their
fields should not be fetched or interpreted. Without that none of the
subsequent HW operations should be performed inside trbe_enable_hw()
leading upto enabling it.

> 
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index f5597bd9b5fba9a8f5053d5823b03380fd468b5c..e426991e2c2c398a9d3982e9d0f7f542e404cbab 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -629,7 +629,6 @@ static void trbe_enable_hw(struct trbe_buf *buf)
>  	WARN_ON(buf->trbe_hw_base < buf->trbe_base);
>  	WARN_ON(buf->trbe_write < buf->trbe_hw_base);
>  	WARN_ON(buf->trbe_write >= buf->trbe_limit);
> -	set_trbe_disabled(buf->cpudata);
>  	clr_trbe_status();
>  	set_trbe_base_pointer(buf->trbe_hw_base);
>  	set_trbe_write_pointer(buf->trbe_write);
>