[PATCH AUTOSEL 5.15 14/16] tools/power turbostat: Fix /dev/cpu_dma_latency warnings

[Sasha Levin]

From: Prarit Bhargava <prarit@xxxxxxxxxx>

[ Upstream commit 40aafc7d58d3544f152a863a0e9863014b6d5d8c ]

When running as non-root the following error is seen in turbostat:

turbostat: fopen /dev/cpu_dma_latency
: Permission denied

turbostat and the man page have information on how to avoid other
permission errors, so these can be fixed the same way.

Provide better /dev/cpu_dma_latency warnings that provide instructions on
how to avoid the error, and update the man page.

Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/power/x86/turbostat/turbostat.8 | 2 ++
 tools/power/x86/turbostat/turbostat.c | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/power/x86/turbostat/turbostat.8 b/tools/power/x86/turbostat/turbostat.8
index 9b17097bc3d7b..b3d4bf08e70b1 100644
--- a/tools/power/x86/turbostat/turbostat.8
+++ b/tools/power/x86/turbostat/turbostat.8
@@ -296,6 +296,8 @@ Alternatively, non-root users can be enabled to run turbostat this way:
 
 # chmod +r /dev/cpu/*/msr
 
+# chmod +r /dev/cpu_dma_latency
+
 .B "turbostat "
 reads hardware counters, but doesn't write them.
 So it will not interfere with the OS or other programs, including
diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index 4f176bbf29f42..84b8a35c91972 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -5237,7 +5237,7 @@ void print_dev_latency(void)
 
 	retval = read(fd, (void *)&value, sizeof(int));
 	if (retval != sizeof(int)) {
-		warn("read %s\n", path);
+		warn("read failed %s\n", path);
 		close(fd);
 		return;
 	}
-- 
2.39.2