Messages in this thread | | | Date | Wed, 7 Jun 2017 23:38:10 +0200 | From | Daniel Lezcano <> | Subject | Re: [PATCH 46/58] clocksource/drivers: Add a new driver for the Atmel ARM TC blocks |
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On Wed, Jun 07, 2017 at 05:09:08PM +0200, Alexandre Belloni wrote: > On 07/06/2017 at 16:17:35 +0200, Daniel Lezcano wrote: > > > > > This driver uses regmap and syscon to be able to probe early in the boot > > > > > and avoid having to switch on the TCB clocksource later. Using regmap also > > > > > means that unused TCB channels may be used by other drivers (PWM for > > > > > example). > > > > > > > > Can you give more details, I fail to understand how regmap and syscon help to > > > > probe sooner than timer_init()? > > > > > > > > > Because before that, the tcb driver relied on atmel_tclib to share the > > > TCBs and it happened way too late, at arch_initcall() time. > > > > So is it still necesary to use regmap? I would like to take the opportunity to > > move the init routine to the common init routine if possible: > > > > https://patchwork.kernel.org/patch/9768845/ > > > > It is still necessary because we want to be able to share the timer > between multiple drivers. For example, you can have the clocksource on > channel 0, clockevent on channel 1 and a pwm on channel 2
The hardware timer can be shared, the channels used in different subsystem.
Each channel are used exclusively.
What is the benefit of regmap? It has a cost, and takes a lock at each read.
For instance:
+static u64 tc_get_cycles(struct clocksource *cs) +{ + u32 lower, upper, tmp; + + do { + regmap_read(tc.regmap, ATMEL_TC_CV(1), &upper); + regmap_read(tc.regmap, ATMEL_TC_CV(0), &lower); + regmap_read(tc.regmap, ATMEL_TC_CV(1), &tmp); + } while (upper != tmp); + + return (upper << 16) | lower; +}
Is:
+static u64 tc_get_cycles(struct clocksource *cs) +{ + u32 lower, upper, tmp; + + do { + regmap_read(tc.regmap, ATMEL_TC_CV(1), &upper); lock(); lot-of-things(); unlock(); + regmap_read(tc.regmap, ATMEL_TC_CV(0), &lower); lock(); lot-of-things(); unlock(); + regmap_read(tc.regmap, ATMEL_TC_CV(1), &tmp); lock(); lot-of-things(); unlock(); + } while (upper != tmp); + + return (upper << 16) | lower; +}
I suggest to look what is in 'lot-of-things()' and especially what is doing regcache_read().
May be you can reconsider the regmap? This driver is the only one use the regmap AFAICT and I don't think it is adequate.
> > > > Can you explain why we have two clocks here? > > > > > > > > > > Each channel have its clock, I can add a comment if you want. > > > > I don't understand. Why do we have two clocks? > > > > One channel is driven by one clock and the second one takes the overflow signal > > from the first one, so no second clock is involved there, no? > > > > Those are the peripheral clocks, they are not used by the counters but > used to be able to read/write the registers.
Mmh, strange. Why is the clk[0]'s rate used in this case?
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