| Message ID | 20171215085247.14946-3-benjamin.gaignard@st.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 15/12/2017 09:52, Benjamin Gaignard wrote: > Rather than use fixed prescaler values compute it to get a clock > as close as possible of 10KHz and a resolution of 0.1ms. > > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> > --- > drivers/clocksource/timer-stm32.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c > index 23a321cca45b..de721d318065 100644 > --- a/drivers/clocksource/timer-stm32.c > +++ b/drivers/clocksource/timer-stm32.c > @@ -37,6 +37,11 @@ > > #define TIM_EGR_UG BIT(0) > > +#define MAX_TIM_PSC 0xFFFF > + > +/* Target a 10KHz clock to get a resolution of 0.1 ms */ > +#define TARGETED_CLK_RATE 10000 > + > static int stm32_clock_event_shutdown(struct clock_event_device *evt) > { > struct timer_of *to = to_timer_of(evt); > @@ -83,7 +88,7 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) > static void __init stm32_clockevent_init(struct timer_of *to) > { > unsigned long max_delta; > - int prescaler; > + unsigned long prescaler; > > to->clkevt.name = "stm32_clockevent"; > to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC; > @@ -96,13 +101,17 @@ static void __init stm32_clockevent_init(struct timer_of *to) > /* Detect whether the timer is 16 or 32 bits */ > writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); > max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); > - if (max_delta == ~0U) { > - prescaler = 1; > + to->clkevt.rating = 50; > + if (max_delta == ~0U) > to->clkevt.rating = 250; > - } else { > - prescaler = 1024; > - to->clkevt.rating = 50; > - } > + > + /* > + * Get the highest possible prescaler value to be as close > + * as possible of TARGETED_CLK_RATE > + */ > + prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to), TARGETED_CLK_RATE); With a 90MHz or 125MHz, the prescaler will be 9000 or 12500, so much more than the 1024 we have today for 16b, and 1 for 32b. Shouldn't the computation be weighted with the bits width ? Otherwise the timer will wrap like: 32bits: before: (2^32 / 90e6) x 1 = 47.72 seconds after: (2^32 / 90e6) x 9000 = 119.3 *hours* ~= 5days 16bits: before: (2^16 / 90e6) x 1024 = 0.745 seconds after: (2^16 / 90e6) x 9000 = 6.55 seconds The patch is ok to target the 10KHz timer rate for 16b with a 1ms resolution wrapping up after 6.55 seconds. But not for the 32bits timer. Furthermore, we can't tell anymore the 32bits timers have a rating of 250 after this patch. Leave the 32bits part as it is and compute the prescaler only in case of 16bits with the target rate, which sounds a reasonable approach. > + if (prescaler > MAX_TIM_PSC) > + prescaler = MAX_TIM_PSC; That can happen only if the clock rate is greater than ~655MHz, that could not happen today as far as I can tell regarding the DT. So if we hit this condition, we should speak up in the log (pr_warn). > writel_relaxed(0, timer_of_base(to) + TIM_ARR); > writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC); Can you fix this prescaler - 1 in order to be consistent with the computation with 16b ? (32b prescaler = 0, 16b prescaler = clk_rate / target ). Thanks. -- Daniel
2017-12-18 10:26 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>: > On 15/12/2017 09:52, Benjamin Gaignard wrote: >> Rather than use fixed prescaler values compute it to get a clock >> as close as possible of 10KHz and a resolution of 0.1ms. >> >> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> >> --- >> drivers/clocksource/timer-stm32.c | 23 ++++++++++++++++------- >> 1 file changed, 16 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c >> index 23a321cca45b..de721d318065 100644 >> --- a/drivers/clocksource/timer-stm32.c >> +++ b/drivers/clocksource/timer-stm32.c >> @@ -37,6 +37,11 @@ >> >> #define TIM_EGR_UG BIT(0) >> >> +#define MAX_TIM_PSC 0xFFFF >> + >> +/* Target a 10KHz clock to get a resolution of 0.1 ms */ >> +#define TARGETED_CLK_RATE 10000 >> + >> static int stm32_clock_event_shutdown(struct clock_event_device *evt) >> { >> struct timer_of *to = to_timer_of(evt); >> @@ -83,7 +88,7 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) >> static void __init stm32_clockevent_init(struct timer_of *to) >> { >> unsigned long max_delta; >> - int prescaler; >> + unsigned long prescaler; >> >> to->clkevt.name = "stm32_clockevent"; >> to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC; >> @@ -96,13 +101,17 @@ static void __init stm32_clockevent_init(struct timer_of *to) >> /* Detect whether the timer is 16 or 32 bits */ >> writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); >> max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); >> - if (max_delta == ~0U) { >> - prescaler = 1; >> + to->clkevt.rating = 50; >> + if (max_delta == ~0U) >> to->clkevt.rating = 250; >> - } else { >> - prescaler = 1024; >> - to->clkevt.rating = 50; >> - } >> + >> + /* >> + * Get the highest possible prescaler value to be as close >> + * as possible of TARGETED_CLK_RATE >> + */ >> + prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to), TARGETED_CLK_RATE); > > With a 90MHz or 125MHz, the prescaler will be 9000 or 12500, so much > more than the 1024 we have today for 16b, and 1 for 32b. > > Shouldn't the computation be weighted with the bits width ? My goal was to get the same resolution (0.1ms) for all the timers so the wrap will depend of the number of bits like you describe below. > > Otherwise the timer will wrap like: > > 32bits: > > before: (2^32 / 90e6) x 1 = 47.72 seconds > after: (2^32 / 90e6) x 9000 = 119.3 *hours* ~= 5days > > 16bits: > > before: (2^16 / 90e6) x 1024 = 0.745 seconds > after: (2^16 / 90e6) x 9000 = 6.55 seconds > > The patch is ok to target the 10KHz timer rate for 16b with a 1ms > resolution wrapping up after 6.55 seconds. But not for the 32bits timer. > Furthermore, we can't tell anymore the 32bits timers have a rating of > 250 after this patch. What is the link between rating and resolution (or wrap) ? Is it a problem to get a long wrap ? > > Leave the 32bits part as it is and compute the prescaler only in case of > 16bits with the target rate, which sounds a reasonable approach. > >> + if (prescaler > MAX_TIM_PSC) >> + prescaler = MAX_TIM_PSC; > > That can happen only if the clock rate is greater than ~655MHz, that > could not happen today as far as I can tell regarding the DT. So if we > hit this condition, we should speak up in the log (pr_warn). It is to be futur proof for next possible SoC but even if prescaler reach this limit it is not a problem the only consequence would be that resolution and wrap change. > >> writel_relaxed(0, timer_of_base(to) + TIM_ARR); >> writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC); > > Can you fix this prescaler - 1 in order to be consistent with the > computation with 16b ? (32b prescaler = 0, 16b prescaler = clk_rate / > target ). In the hardware the clock is divise by " TIM_PSC value 1" so to be coherent with that I need to do prescaler -1. Benjamin > > Thanks. > > -- Daniel > > -- > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs > > Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | > <http://twitter.com/#!/linaroorg> Twitter | > <http://www.linaro.org/linaro-blog/> Blog >
On 18/12/2017 10:44, Benjamin Gaignard wrote: > 2017-12-18 10:26 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>: >> On 15/12/2017 09:52, Benjamin Gaignard wrote: >>> Rather than use fixed prescaler values compute it to get a clock >>> as close as possible of 10KHz and a resolution of 0.1ms. >>> >>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> >>> --- >>> drivers/clocksource/timer-stm32.c | 23 ++++++++++++++++------- >>> 1 file changed, 16 insertions(+), 7 deletions(-) >>> >>> diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c >>> index 23a321cca45b..de721d318065 100644 >>> --- a/drivers/clocksource/timer-stm32.c >>> +++ b/drivers/clocksource/timer-stm32.c >>> @@ -37,6 +37,11 @@ >>> >>> #define TIM_EGR_UG BIT(0) >>> >>> +#define MAX_TIM_PSC 0xFFFF >>> + >>> +/* Target a 10KHz clock to get a resolution of 0.1 ms */ >>> +#define TARGETED_CLK_RATE 10000 >>> + >>> static int stm32_clock_event_shutdown(struct clock_event_device *evt) >>> { >>> struct timer_of *to = to_timer_of(evt); >>> @@ -83,7 +88,7 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) >>> static void __init stm32_clockevent_init(struct timer_of *to) >>> { >>> unsigned long max_delta; >>> - int prescaler; >>> + unsigned long prescaler; >>> >>> to->clkevt.name = "stm32_clockevent"; >>> to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC; >>> @@ -96,13 +101,17 @@ static void __init stm32_clockevent_init(struct timer_of *to) >>> /* Detect whether the timer is 16 or 32 bits */ >>> writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); >>> max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); >>> - if (max_delta == ~0U) { >>> - prescaler = 1; >>> + to->clkevt.rating = 50; >>> + if (max_delta == ~0U) >>> to->clkevt.rating = 250; >>> - } else { >>> - prescaler = 1024; >>> - to->clkevt.rating = 50; >>> - } >>> + >>> + /* >>> + * Get the highest possible prescaler value to be as close >>> + * as possible of TARGETED_CLK_RATE >>> + */ >>> + prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to), TARGETED_CLK_RATE); >> >> With a 90MHz or 125MHz, the prescaler will be 9000 or 12500, so much >> more than the 1024 we have today for 16b, and 1 for 32b. >> >> Shouldn't the computation be weighted with the bits width ? > > My goal was to get the same resolution (0.1ms) for all the timers so > the wrap will depend of the number of bits like you describe below. Do you really want 1ms resolution with a 32bits timer ? >> Otherwise the timer will wrap like: >> >> 32bits: >> >> before: (2^32 / 90e6) x 1 = 47.72 seconds >> after: (2^32 / 90e6) x 9000 = 119.3 *hours* ~= 5days >> >> 16bits: >> >> before: (2^16 / 90e6) x 1024 = 0.745 seconds >> after: (2^16 / 90e6) x 9000 = 6.55 seconds >> >> The patch is ok to target the 10KHz timer rate for 16b with a 1ms >> resolution wrapping up after 6.55 seconds. But not for the 32bits timer. >> Furthermore, we can't tell anymore the 32bits timers have a rating of >> 250 after this patch. > > What is the link between rating and resolution (or wrap) ? Low resolution => hardly suitable for real use case => bad rating. From include/linux/clocksource.h [ ... ] * 100-199: Base level usability. * Functional for real use, but not desired. * 200-299: Good. * A correct and usable clocksource. [ ... ] If you want to set a timer with a delta of 12.345ms and the resolution is 1ms. Then you end up with a timer expiring after 13ms. > Is it a problem to get a long wrap ? It is not a problem to go for a long wrap, it is usually interesting when the CPU has deep idle states. But it is not worth to sacrifice the resolution with the 32bits timer in order to have 5 days before wrap. Keeping 47secs is fine for the moment. If you want a coarser grain, that could be acceptable because the resolution is very high but we can postpone that for later after solving this 16b / 32b thing. >> Leave the 32bits part as it is and compute the prescaler only in case of >> 16bits with the target rate, which sounds a reasonable approach. >> >>> + if (prescaler > MAX_TIM_PSC) >>> + prescaler = MAX_TIM_PSC; >> >> That can happen only if the clock rate is greater than ~655MHz, that >> could not happen today as far as I can tell regarding the DT. So if we >> hit this condition, we should speak up in the log (pr_warn). > > It is to be futur proof for next possible SoC but even if prescaler > reach this limit > it is not a problem the only consequence would be that resolution and > wrap change. Got that, but that needs to be logged with a pr_warn or pr_info. >>> writel_relaxed(0, timer_of_base(to) + TIM_ARR); >>> writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC); >> >> Can you fix this prescaler - 1 in order to be consistent with the >> computation with 16b ? (32b prescaler = 0, 16b prescaler = clk_rate / >> target ). > > In the hardware the clock is divise by " TIM_PSC value 1" so to be coherent > with that I need to do prescaler -1. Ah, ok.
2017-12-18 11:54 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>: > On 18/12/2017 10:44, Benjamin Gaignard wrote: >> 2017-12-18 10:26 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>: >>> On 15/12/2017 09:52, Benjamin Gaignard wrote: >>>> Rather than use fixed prescaler values compute it to get a clock >>>> as close as possible of 10KHz and a resolution of 0.1ms. >>>> >>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> >>>> --- >>>> drivers/clocksource/timer-stm32.c | 23 ++++++++++++++++------- >>>> 1 file changed, 16 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c >>>> index 23a321cca45b..de721d318065 100644 >>>> --- a/drivers/clocksource/timer-stm32.c >>>> +++ b/drivers/clocksource/timer-stm32.c >>>> @@ -37,6 +37,11 @@ >>>> >>>> #define TIM_EGR_UG BIT(0) >>>> >>>> +#define MAX_TIM_PSC 0xFFFF >>>> + >>>> +/* Target a 10KHz clock to get a resolution of 0.1 ms */ >>>> +#define TARGETED_CLK_RATE 10000 >>>> + >>>> static int stm32_clock_event_shutdown(struct clock_event_device *evt) >>>> { >>>> struct timer_of *to = to_timer_of(evt); >>>> @@ -83,7 +88,7 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) >>>> static void __init stm32_clockevent_init(struct timer_of *to) >>>> { >>>> unsigned long max_delta; >>>> - int prescaler; >>>> + unsigned long prescaler; >>>> >>>> to->clkevt.name = "stm32_clockevent"; >>>> to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC; >>>> @@ -96,13 +101,17 @@ static void __init stm32_clockevent_init(struct timer_of *to) >>>> /* Detect whether the timer is 16 or 32 bits */ >>>> writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); >>>> max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); >>>> - if (max_delta == ~0U) { >>>> - prescaler = 1; >>>> + to->clkevt.rating = 50; >>>> + if (max_delta == ~0U) >>>> to->clkevt.rating = 250; >>>> - } else { >>>> - prescaler = 1024; >>>> - to->clkevt.rating = 50; >>>> - } >>>> + >>>> + /* >>>> + * Get the highest possible prescaler value to be as close >>>> + * as possible of TARGETED_CLK_RATE >>>> + */ >>>> + prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to), TARGETED_CLK_RATE); >>> >>> With a 90MHz or 125MHz, the prescaler will be 9000 or 12500, so much >>> more than the 1024 we have today for 16b, and 1 for 32b. >>> >>> Shouldn't the computation be weighted with the bits width ? >> >> My goal was to get the same resolution (0.1ms) for all the timers so >> the wrap will depend of the number of bits like you describe below. > > Do you really want 1ms resolution with a 32bits timer ? I want a resolution of 0.1 ms (TARGETED_CLK_RATE = 10.000) for all the timers or 0.01ms if you think is better. > >>> Otherwise the timer will wrap like: >>> >>> 32bits: >>> >>> before: (2^32 / 90e6) x 1 = 47.72 seconds >>> after: (2^32 / 90e6) x 9000 = 119.3 *hours* ~= 5days >>> >>> 16bits: >>> >>> before: (2^16 / 90e6) x 1024 = 0.745 seconds >>> after: (2^16 / 90e6) x 9000 = 6.55 seconds >>> >>> The patch is ok to target the 10KHz timer rate for 16b with a 1ms >>> resolution wrapping up after 6.55 seconds. But not for the 32bits timer. >>> Furthermore, we can't tell anymore the 32bits timers have a rating of >>> 250 after this patch. >> >> What is the link between rating and resolution (or wrap) ? > > Low resolution => hardly suitable for real use case => bad rating. > > From include/linux/clocksource.h > > [ ... ] > > * 100-199: Base level usability. > * Functional for real use, but not desired. > * 200-299: Good. > * A correct and usable clocksource. > > [ ... ] > > If you want to set a timer with a delta of 12.345ms and the resolution > is 1ms. Then you end up with a timer expiring after 13ms. > >> Is it a problem to get a long wrap ? > > It is not a problem to go for a long wrap, it is usually interesting > when the CPU has deep idle states. But it is not worth to sacrifice the > resolution with the 32bits timer in order to have 5 days before wrap. > > Keeping 47secs is fine for the moment. If you want a coarser grain, that > could be acceptable because the resolution is very high but we can > postpone that for later after solving this 16b / 32b thing. When the resolution is too high I have issues with min delta value because CPU can handle interrupt each 11ns. > >>> Leave the 32bits part as it is and compute the prescaler only in case of >>> 16bits with the target rate, which sounds a reasonable approach. >>> >>>> + if (prescaler > MAX_TIM_PSC) >>>> + prescaler = MAX_TIM_PSC; >>> >>> That can happen only if the clock rate is greater than ~655MHz, that >>> could not happen today as far as I can tell regarding the DT. So if we >>> hit this condition, we should speak up in the log (pr_warn). >> >> It is to be futur proof for next possible SoC but even if prescaler >> reach this limit >> it is not a problem the only consequence would be that resolution and >> wrap change. > > Got that, but that needs to be logged with a pr_warn or pr_info. OK > >>>> writel_relaxed(0, timer_of_base(to) + TIM_ARR); >>>> writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC); >>> >>> Can you fix this prescaler - 1 in order to be consistent with the >>> computation with 16b ? (32b prescaler = 0, 16b prescaler = clk_rate / >>> target ). >> >> In the hardware the clock is divise by " TIM_PSC value 1" so to be coherent >> with that I need to do prescaler -1. > > Ah, ok. > > > -- > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs > > Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | > <http://twitter.com/#!/linaroorg> Twitter | > <http://www.linaro.org/linaro-blog/> Blog >
diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c index 23a321cca45b..de721d318065 100644 --- a/drivers/clocksource/timer-stm32.c +++ b/drivers/clocksource/timer-stm32.c @@ -37,6 +37,11 @@ #define TIM_EGR_UG BIT(0) +#define MAX_TIM_PSC 0xFFFF + +/* Target a 10KHz clock to get a resolution of 0.1 ms */ +#define TARGETED_CLK_RATE 10000 + static int stm32_clock_event_shutdown(struct clock_event_device *evt) { struct timer_of *to = to_timer_of(evt); @@ -83,7 +88,7 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) static void __init stm32_clockevent_init(struct timer_of *to) { unsigned long max_delta; - int prescaler; + unsigned long prescaler; to->clkevt.name = "stm32_clockevent"; to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC; @@ -96,13 +101,17 @@ static void __init stm32_clockevent_init(struct timer_of *to) /* Detect whether the timer is 16 or 32 bits */ writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); - if (max_delta == ~0U) { - prescaler = 1; + to->clkevt.rating = 50; + if (max_delta == ~0U) to->clkevt.rating = 250; - } else { - prescaler = 1024; - to->clkevt.rating = 50; - } + + /* + * Get the highest possible prescaler value to be as close + * as possible of TARGETED_CLK_RATE + */ + prescaler = DIV_ROUND_CLOSEST(timer_of_rate(to), TARGETED_CLK_RATE); + if (prescaler > MAX_TIM_PSC) + prescaler = MAX_TIM_PSC; writel_relaxed(0, timer_of_base(to) + TIM_ARR); writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC);
Rather than use fixed prescaler values compute it to get a clock as close as possible of 10KHz and a resolution of 0.1ms. Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> --- drivers/clocksource/timer-stm32.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)