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| author | Doug Brown <doug@schmorgal.com> | 2022-12-03 16:51:17 -0800 |
|---|---|---|
| committer | Arnd Bergmann <arnd@arndb.de> | 2022-12-04 13:11:40 +0100 |
| commit | e348b4014c31041e13ff370669ba3348c4d385e3 (patch) | |
| tree | 30dfcc77efd3a3f8e2a2be9da5d6aa467de63797 /arch/arm/mach-mmp | |
| parent | 1d9ae5a1356a61cef94b34e4ccb28986955e2fd2 (diff) | |
| download | linux-e348b4014c31041e13ff370669ba3348c4d385e3.tar.bz2 | |
ARM: mmp: fix timer_read delay
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>
Diffstat (limited to 'arch/arm/mach-mmp')
| -rw-r--r-- | arch/arm/mach-mmp/time.c | 11 |
1 files 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) |