linux-kernel - [PATCH] perf cs-etm: add error logging to cs_etm_is

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Date:   Thu, 2 Mar 2023 17:29:28 +0800
From:   Junhao He <hejunhao3@...wei.com>
To:     <will@...nel.org>, <linux-kernel@...r.kernel.org>,
        <jonathan.cameron@...wei.com>, <mark.rutland@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <zhangshaokun@...ilicon.com>, <catalin.marinas@....com>,
        <kernel-team@...roid.com>, <linuxarm@...wei.com>,
        <yangyicong@...wei.com>, <f.fangjian@...wei.com>,
        <shenyang39@...wei.com>, <prime.zeng@...ilicon.com>,
        <hejunhao3@...wei.com>
Subject: [PATCH] perf cs-etm: add error logging to cs_etm_is_etmv4()

On the HiSilicon platform, there is one ETM per logic core.
When setting up SMT, not every process has an ETM. So the path
".../cs_etm/cpux/trcidr/trcidr0" does not exist, the function
perf_pmu__scan_file() return an error. However, the command
'perf record' will returns silently and don't print.

After this patch, log a error when read fails that makes it easy
for users to debug.

  root@...alhost:/# perf record -e /cs_etm/@...ra_smb0/ -C 3 uname -a
  cs_etm: can't read file cpu3/trcidr/trcidr0
  root@...alhost:/#

Signed-off-by: Junhao He <hejunhao3@...wei.com>
---
 tools/perf/arch/arm/util/cs-etm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
index 7f71c8a237ff..19ea17430399 100644
--- a/tools/perf/arch/arm/util/cs-etm.c
+++ b/tools/perf/arch/arm/util/cs-etm.c
@@ -585,7 +585,6 @@ cs_etm_info_priv_size(struct auxtrace_record *itr __maybe_unused,
 
 static bool cs_etm_is_etmv4(struct auxtrace_record *itr, int cpu)
 {
-	bool ret = false;
 	char path[PATH_MAX];
 	int scan;
 	unsigned int val;
@@ -600,9 +599,10 @@ static bool cs_etm_is_etmv4(struct auxtrace_record *itr, int cpu)
 
 	/* The file was read successfully, we have a winner */
 	if (scan == 1)
-		ret = true;
+		return true;
 
-	return ret;
+	pr_err("%s: can't read file %s\n", CORESIGHT_ETM_PMU_NAME, path);
+	return false;
 }
 
 static int cs_etm_get_ro(struct perf_pmu *pmu, int cpu, const char *path)
-- 
2.33.0