linux-kernel - [PATCH] clocksource/fsl: Fix errata A-007728 for flextimer

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Date:   Thu, 8 Sep 2016 10:04:55 +0800
From:   Meng Yi <meng.yi@....com>
To:     <daniel.lezcano@...aro.org>, <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>
CC:     Meng Yi <meng.yi@....com>
Subject: [PATCH] clocksource/fsl: Fix errata A-007728 for flextimer

If the FTM counter reaches the FTM_MOD value between the reading of the
TOF bit and the writing of 0 to the TOF bit, the process of clearing the
TOF bit does not work as expected when FTMx_CONF[NUMTOF] != 0 and the
current TOF count is less than FTMx_CONF[NUMTOF]. If the above condition
is met, the TOF bit remains set. If the TOF interrupt is enabled
(FTMx_SC[TOIE] = 1), the TOF interrupt also remains asserted.

Above is the errata discription

The workaround is clearing TOF bit until it is cleaned(FTM counter doesn't
always reache the FTM_MOD anyway),which may cost some cycles.

Signed-off-by: Meng Yi <meng.yi@....com>
---
 drivers/clocksource/fsl_ftm_timer.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/clocksource/fsl_ftm_timer.c b/drivers/clocksource/fsl_ftm_timer.c
index 738515b..ade26e5 100644
--- a/drivers/clocksource/fsl_ftm_timer.c
+++ b/drivers/clocksource/fsl_ftm_timer.c
@@ -83,11 +83,10 @@ static inline void ftm_counter_disable(void __iomem *base)

 static inline void ftm_irq_acknowledge(void __iomem *base)
 {
-	u32 val;
-
-	val = ftm_readl(base + FTM_SC);
-	val &= ~FTM_SC_TOF;
-	ftm_writel(val, base + FTM_SC);
+	/*read and clean the FTM_SC_TOF bit until its cleared*/
+	while (FTM_SC_TOF & ftm_readl(base + FTM_SC))
+		ftm_writel(ftm_readl(base + FTM_SC) & (~FTM_SC_TOF),
+			   base + FTM_SC);
 }

 static inline void ftm_irq_enable(void __iomem *base)
-- 
2.1.0.27.g96db324