linux-kernel - Re: [PATCH 11/19] coresight: trbe: Apply overwrite erratum for only wrap event

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Message-ID: <20251202171233.GF724103@e132581.arm.com>
Date: Tue, 2 Dec 2025 17:12:33 +0000
From: Leo Yan <leo.yan@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	James Clark <james.clark@...aro.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	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>, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 11/19] coresight: trbe: Apply overwrite erratum for only
 wrap event

On Tue, Dec 02, 2025 at 04:56:47PM +0000, Coresight ML wrote:
> On Tue, Dec 02, 2025 at 12:05:52PM +0000, Suzuki K Poulose wrote:
> > On 01/12/2025 11:22, Leo Yan wrote:
> > > The overwrite erratum occurs only on wrap events, so apply the extra
> > > wrap condition check in the workaround.
> > > 
> > > Signed-off-by: Leo Yan <leo.yan@....com>
> > > ---
> > >   drivers/hwtracing/coresight/coresight-trbe.c | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> > > index e579ea98523c24d23a0cd265dcdd0a46b52b52da..2600af12a8fb94bb8c74efda2a101aacd01b0b34 100644
> > > --- a/drivers/hwtracing/coresight/coresight-trbe.c
> > > +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> > > @@ -714,7 +714,7 @@ static unsigned long trbe_get_trace_size(struct perf_output_handle *handle,
> > >   	 * 64bytes. Thus we ignore the potential triggering of the erratum
> > >   	 * on WRAP and limit the data to LIMIT.
> > >   	 */
> > > -	if (wrap)
> > > +	if (wrap && trbe_may_overwrite_in_fill_mode(buf->cpudata))
> > >   		write = get_trbe_limit_pointer();
> > 
> > This must be trbe_may_write_out_of_range() ?
> 
> SDEN (e.g., [1]) is ambiguous about how the write pointer acts for the
> out-of-range erratum.

Thought again, we should not worry about out-of-range case.

As the workaround always ensures sufficient space beyond the limit, the
write pointer remains valid within the allocated buffer even if it is
updated and crosses that limit.