linux-kernel - [PATCH AUTOSEL 5.5 21/41] drivers/perf: fsl_imx8

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Date:   Sun, 15 Mar 2020 22:32:59 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Joakim Zhang <qiangqing.zhang@....com>,
        Will Deacon <will@...nel.org>, Sasha Levin <sashal@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH AUTOSEL 5.5 21/41] drivers/perf: fsl_imx8_ddr: Correct the CLEAR bit definition

From: Joakim Zhang <qiangqing.zhang@....com>

[ Upstream commit 049d919168458ac54e7fad27cd156a958b042d2f ]

When disabling a counter from ddr_perf_event_stop(), the counter value
is reset to 0 at the same time.

Preserve the counter value by performing a read-modify-write of the
PMU register and clearing only the enable bit.

Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/perf/fsl_imx8_ddr_perf.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/perf/fsl_imx8_ddr_perf.c b/drivers/perf/fsl_imx8_ddr_perf.c
index 95dca2cb52650..90884d14f95fa 100644
--- a/drivers/perf/fsl_imx8_ddr_perf.c
+++ b/drivers/perf/fsl_imx8_ddr_perf.c
@@ -388,9 +388,10 @@ static void ddr_perf_counter_enable(struct ddr_pmu *pmu, int config,
 
 	if (enable) {
 		/*
-		 * must disable first, then enable again
-		 * otherwise, cycle counter will not work
-		 * if previous state is enabled.
+		 * cycle counter is special which should firstly write 0 then
+		 * write 1 into CLEAR bit to clear it. Other counters only
+		 * need write 0 into CLEAR bit and it turns out to be 1 by
+		 * hardware. Below enable flow is harmless for all counters.
 		 */
 		writel(0, pmu->base + reg);
 		val = CNTL_EN | CNTL_CLEAR;
@@ -398,7 +399,8 @@ static void ddr_perf_counter_enable(struct ddr_pmu *pmu, int config,
 		writel(val, pmu->base + reg);
 	} else {
 		/* Disable counter */
-		writel(0, pmu->base + reg);
+		val = readl_relaxed(pmu->base + reg) & CNTL_EN_MASK;
+		writel(val, pmu->base + reg);
 	}
 }
 
-- 
2.20.1