From 3c6dfce2c76c46dd555d2c91e2797d572a497d48 Mon Sep 17 00:00:00 2001 From: Doug Brown Date: Sat, 3 Dec 2022 16:51:17 -0800 Subject: [PATCH] ARM: mmp: fix timer_read delay [ Upstream commit e348b4014c31041e13ff370669ba3348c4d385e3 ] timer_read() was using an empty 100-iteration loop to wait for the TMR_CVWR register to capture the latest timer counter value. The delay wasn't long enough. This resulted in CPU idle time being extremely underreported on PXA168 with CONFIG_NO_HZ_IDLE=y. Switch to the approach used in the vendor kernel, which implements the capture delay by reading TMR_CVWR a few times instead. Fixes: 49cbe78637eb ("[ARM] pxa: add base support for Marvell's PXA168 processor line") Signed-off-by: Doug Brown Link: https://lore.kernel.org/r/20221204005117.53452-3-doug@schmorgal.com Signed-off-by: Arnd Bergmann Signed-off-by: Sasha Levin --- arch/arm/mach-mmp/time.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/arm/mach-mmp/time.c b/arch/arm/mach-mmp/time.c index 41b2e8abc9e6..708816caf859 100644 --- a/arch/arm/mach-mmp/time.c +++ b/arch/arm/mach-mmp/time.c @@ -43,18 +43,21 @@ static void __iomem *mmp_timer_base = TIMERS_VIRT_BASE; /* - * FIXME: the timer needs some delay to stablize the counter capture + * Read the timer through the CVWR register. Delay is required after requesting + * a read. The CR register cannot be directly read due to metastability issues + * documented in the PXA168 software manual. */ static inline uint32_t timer_read(void) { - int delay = 100; + uint32_t val; + int delay = 3; __raw_writel(1, mmp_timer_base + TMR_CVWR(1)); while (delay--) - cpu_relax(); + val = __raw_readl(mmp_timer_base + TMR_CVWR(1)); - return __raw_readl(mmp_timer_base + TMR_CVWR(1)); + return val; } static u64 notrace mmp_read_sched_clock(void)