From: Doug Brown doug@schmorgal.com
[ 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 doug@schmorgal.com Link: https://lore.kernel.org/r/20221204005117.53452-3-doug@schmorgal.com Signed-off-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Sasha Levin sashal@kernel.org --- 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 483df32583be..0bdb872f5018 100644 --- a/arch/arm/mach-mmp/time.c +++ b/arch/arm/mach-mmp/time.c @@ -44,18 +44,21 @@ 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)