Messages in this thread | | | Date | Tue, 12 Nov 2013 20:01:37 +0100 | From | Daniel Lezcano <> | Subject | Re: [PATCH 5/7] clocksource/cadence_ttc: Overhaul clocksource frequency adjustment |
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On 11/08/2013 10:21 PM, Soren Brinkmann wrote: > The currently used method adjusting the clocksource to a changing input > frequency does not work on kernels from 3.11 on. > The new approach is to keep the timer frequency as constant as possible. > I.e. > - due to the TTC's prescaler limitations, allow frequency changes > only if the frequency scales by a power of 2 > - adjust the counter's divider on the fly when a frequency change > occurs > > When suspending though, the driver should not prevent rate changes in > order to allow the system to enter its low power state. For that > reason a PM notifier is added so rate changes can be ignored during > suspend/resume.
It sounds very weird you have to add a PM notifier in this driver.
Have you been facing an issue or do you assume it could happen ?
> This limits cpufreq to scale by certain factors only. > But we may keep the time base somewhat constant, so that sleep() & co > keep working as expected, while supporting cpufreq and suspend. > > Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com> > --- > drivers/clocksource/cadence_ttc_timer.c | 142 +++++++++++++++++++++++++++----- > 1 file changed, 122 insertions(+), 20 deletions(-) > > diff --git a/drivers/clocksource/cadence_ttc_timer.c b/drivers/clocksource/cadence_ttc_timer.c > index 68a336038d8f..421b942dd707 100644 > --- a/drivers/clocksource/cadence_ttc_timer.c > +++ b/drivers/clocksource/cadence_ttc_timer.c > @@ -16,12 +16,14 @@ > */ > > #include <linux/clk.h> > +#include <linux/clk-provider.h> > #include <linux/interrupt.h> > #include <linux/clockchips.h> > #include <linux/of_address.h> > #include <linux/of_irq.h> > #include <linux/slab.h> > #include <linux/sched_clock.h> > +#include <linux/suspend.h> > > /* > * This driver configures the 2 16-bit count-up timers as follows: > @@ -52,6 +54,8 @@ > #define TTC_CNT_CNTRL_DISABLE_MASK 0x1 > > #define TTC_CLK_CNTRL_CSRC_MASK (1 << 5) /* clock source */ > +#define TTC_CLK_CNTRL_PSV_MASK 0x1e > +#define TTC_CLK_CNTRL_PSV_SHIFT 1 > > /* > * Setup the timers to use pre-scaling, using a fixed value for now that will > @@ -63,6 +67,8 @@ > #define CLK_CNTRL_PRESCALE_EN 1 > #define CNT_CNTRL_RESET (1 << 4) > > +#define MAX_F_ERR 50 > + > /** > * struct ttc_timer - This definition defines local timer structure > * > @@ -82,8 +88,13 @@ struct ttc_timer { > container_of(x, struct ttc_timer, clk_rate_change_nb) > > struct ttc_timer_clocksource { > + int scale_dir; > + u32 scale_clk_ctrl_reg_old; > + u32 scale_clk_ctrl_reg_new; > + int suspending; > struct ttc_timer ttc; > struct clocksource cs; > + struct notifier_block suspend_nb; > }; > > #define to_ttc_timer_clksrc(x) \ > @@ -228,33 +239,120 @@ static int ttc_rate_change_clocksource_cb(struct notifier_block *nb, > struct ttc_timer_clocksource *ttccs = container_of(ttc, > struct ttc_timer_clocksource, ttc); > > + if (ttccs->suspending) > + return NOTIFY_OK;
I don't see how it couldn't be racy. What prevents suspend to occur right after this check ?
> + > switch (event) { > - case POST_RATE_CHANGE: > + case PRE_RATE_CHANGE: > + { > + u32 psv; > + unsigned long factor, rate_low, rate_high; > + > + if (ndata->new_rate == ndata->old_rate) { > + ttccs->scale_dir = 0; > + return NOTIFY_OK; > + } > + > + if (ndata->new_rate > ndata->old_rate) { > + factor = DIV_ROUND_CLOSEST(ndata->new_rate, > + ndata->old_rate); > + ttccs->scale_dir = 1; > + rate_low = ndata->old_rate; > + rate_high = ndata->new_rate; > + } else { > + factor = DIV_ROUND_CLOSEST(ndata->old_rate, > + ndata->new_rate); > + ttccs->scale_dir = -1; > + rate_low = ndata->new_rate; > + rate_high = ndata->old_rate; > + }
Hmm, it could be interesting if Viresh can give its opinion on this patch [cc'ed].
> + > + if (!is_power_of_2(factor)) > + return NOTIFY_BAD; > + > + if (abs(rate_high - (factor * rate_low)) > MAX_F_ERR) > + return NOTIFY_BAD; > + > + factor = __ilog2_u32(factor); > + > /* > - * Do whatever is necessary to maintain a proper time base > - * > - * I cannot find a way to adjust the currently used clocksource > - * to the new frequency. __clocksource_updatefreq_hz() sounds > - * good, but does not work. Not sure what's that missing. > - * > - * This approach works, but triggers two clocksource switches. > - * The first after unregister to clocksource jiffies. And > - * another one after the register to the newly registered timer. > - * > - * Alternatively we could 'waste' another HW timer to ping pong > - * between clock sources. That would also use one register and > - * one unregister call, but only trigger one clocksource switch > - * for the cost of another HW timer used by the OS. > + * store timer clock ctrl register so we can restore it in case > + * of an abort. > */ > - clocksource_unregister(&ttccs->cs); > - clocksource_register_hz(&ttccs->cs, > - ndata->new_rate / PRESCALE); > - /* fall through */ > - case PRE_RATE_CHANGE: > + ttccs->scale_clk_ctrl_reg_old = > + __raw_readl(ttccs->ttc.base_addr + > + TTC_CLK_CNTRL_OFFSET); > + > + psv = (ttccs->scale_clk_ctrl_reg_old & > + TTC_CLK_CNTRL_PSV_MASK) >> > + TTC_CLK_CNTRL_PSV_SHIFT; > + if (ttccs->scale_dir < 0) > + psv -= factor; > + else > + psv += factor; > + > + /* prescaler within legal range? */ > + if (psv & ~(TTC_CLK_CNTRL_PSV_MASK >> TTC_CLK_CNTRL_PSV_SHIFT)) > + return NOTIFY_BAD; > + > + ttccs->scale_clk_ctrl_reg_new = ttccs->scale_clk_ctrl_reg_old & > + ~TTC_CLK_CNTRL_PSV_MASK; > + ttccs->scale_clk_ctrl_reg_new |= psv << TTC_CLK_CNTRL_PSV_SHIFT; > + > + > + /* scale down: adjust divider in post-change notification */ > + if (ttccs->scale_dir < 0) > + return NOTIFY_DONE; > + > + /* scale up: adjust divider now - before frequency change */ > + __raw_writel(ttccs->scale_clk_ctrl_reg_new, > + ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET); > + break; > + } > + case POST_RATE_CHANGE: > + /* scale up: pre-change notification did the adjustment */ > + if (ttccs->scale_dir >= 0) > + return NOTIFY_OK; > + > + /* scale down: adjust divider now - after frequency change */ > + __raw_writel(ttccs->scale_clk_ctrl_reg_new, > + ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET); > + break; > + > case ABORT_RATE_CHANGE: > + /* we have to undo the adjustment in case we scale up */ > + if (ttccs->scale_dir <= 0) > + return NOTIFY_OK; > + > + /* restore original register value */ > + __raw_writel(ttccs->scale_clk_ctrl_reg_old, > + ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET); > + /* fall through */ > default: > return NOTIFY_DONE; > } > + > + return NOTIFY_DONE; > +} > + > +static int ttc_suspend_notifier_cb(struct notifier_block *nb, > + unsigned long event, void *data) > +{ > + struct ttc_timer_clocksource *ttccs = container_of(nb, > + struct ttc_timer_clocksource, suspend_nb); > + > + switch (event) { > + case PM_SUSPEND_PREPARE: > + ttccs->suspending = 1; > + break; > + case PM_POST_SUSPEND: > + ttccs->suspending = 0; > + break; > + default: > + break; > + } > + > + return NOTIFY_DONE; > } > > static void __init ttc_setup_clocksource(struct clk *clk, void __iomem *base) > @@ -283,6 +381,10 @@ static void __init ttc_setup_clocksource(struct clk *clk, void __iomem *base) > &ttccs->ttc.clk_rate_change_nb)) > pr_warn("Unable to register clock notifier.\n"); > > + ttccs->suspend_nb.notifier_call = ttc_suspend_notifier_cb; > + if (register_pm_notifier(&ttccs->suspend_nb)) > + pr_warn("Unable to register PM notifier.\n"); > + > ttccs->ttc.base_addr = base; > ttccs->cs.name = "ttc_clocksource"; > ttccs->cs.rating = 200; >
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