On Fri, Nov 20, 2020 at 04:57:31PM +0100, Sylwester Nawrocki wrote: > The PLL status polling loops in the set_rate callbacks of some PLLs > have no timeout detection and may become endless loops when something > goes wrong with the PLL. > > For some PLLs there is already the ktime API based timeout detection, > but it will not work in all conditions when .set_rate gets called. > In particular, before the clocksource is initialized or when the > timekeeping is suspended. > > This patch adds a common helper with the PLL status bit polling and > timeout detection. For conditions where the timekeeping API should not > be used a simple readl_relaxed/cpu_relax() busy loop is added with the > iterations limit derived from measurements of readl_relaxed() execution > time for various PLL types and Exynos SoCs variants. > > Actual PLL lock time depends on the P divider value, the VCO frequency > and a constant PLL type specific LOCK_FACTOR and can be calculated as > > lock_time = Pdiv * LOCK_FACTOR / VCO_freq > > For the ktime API use cases a common timeout value of 20 ms is applied > for all the PLLs with an assumption that maximum possible value of Pdiv > is 64, maximum possible LOCK_FACTOR value is 3000 and minimum VCO > frequency is 24 MHz. > > Signed-off-by: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> Reviewed-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx> Best regards, Krzysztof
