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clocksource/cadence_ttc: Overhaul clocksource frequency adjustment 

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

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.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Michal Simek <michal.simek@xilinx.com>
This commit is contained in:
Soren Brinkmann 2014-02-19 15:14:42 -08:00 committed by Daniel Lezcano
parent 5f0ba3b462
commit b3e90722f6
1 changed files with 85 additions and 21 deletions
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106
drivers/clocksource/cadence_ttc_timer.c
View File

@ -16,6 +16,7 @@
*/
#include <linux/clk.h>
#include <linux/clk-provider.h>
#include <linux/interrupt.h>
#include <linux/clockchips.h>
#include <linux/of_address.h>
@ -52,6 +53,8 @@
#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 +66,8 @@
#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
*
@ -82,6 +87,8 @@ struct ttc_timer {
container_of(x, struct ttc_timer, clk_rate_change_nb)
struct ttc_timer_clocksource {
u32 scale_clk_ctrl_reg_old;
u32 scale_clk_ctrl_reg_new;
struct ttc_timer ttc;
struct clocksource cs;
};
@ -229,32 +236,89 @@ static int ttc_rate_change_clocksource_cb(struct notifier_block *nb,
struct ttc_timer_clocksource, ttc);
switch (event) {
case POST_RATE_CHANGE:
/*
* 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.
*/
clocksource_unregister(&ttccs->cs);
clocksource_register_hz(&ttccs->cs,
ndata->new_rate / PRESCALE);
/* fall through */
case PRE_RATE_CHANGE:
{
u32 psv;
unsigned long factor, rate_low, rate_high;
if (ndata->new_rate > ndata->old_rate) {
factor = DIV_ROUND_CLOSEST(ndata->new_rate,
ndata->old_rate);
rate_low = ndata->old_rate;
rate_high = ndata->new_rate;
} else {
factor = DIV_ROUND_CLOSEST(ndata->old_rate,
ndata->new_rate);
rate_low = ndata->new_rate;
rate_high = ndata->old_rate;
}
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);
/*
* store timer clock ctrl register so we can restore it in case
* of an abort.
*/
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 (ndata->new_rate < ndata->old_rate)
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 (ndata->new_rate < ndata->old_rate)
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 (ndata->new_rate > ndata->old_rate)
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 (ndata->new_rate < ndata->old_rate)
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 void __init ttc_setup_clocksource(struct clk *clk, void __iomem *base)