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@xxxxxxxxxx> --- 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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