[PATCH] tcb_clksrc: Use 32 bit tcb as sched_clock
Nicolas Ferre
nicolas.ferre at atmel.com
Tue Jan 24 05:39:10 PST 2017
Le 11/01/2017 à 14:50, David Engraf a écrit :
> On newer boards the TC can be read as single 32 bit value without locking.
> Thus the clock can be used as reference for sched_clock which is much more
> accurate than the jiffies implementation.
>
> Tested on a Atmel SAMA5D2 board.
>
> Signed-off-by: David Engraf <david.engraf at sysgo.com>
Acked-by: Nicolas Ferre <nicolas.ferre at atmel.com>
Thanks,
> ---
> drivers/clocksource/tcb_clksrc.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/tcb_clksrc.c b/drivers/clocksource/tcb_clksrc.c
> index d4ca996..745844e 100644
> --- a/drivers/clocksource/tcb_clksrc.c
> +++ b/drivers/clocksource/tcb_clksrc.c
> @@ -10,6 +10,7 @@
> #include <linux/io.h>
> #include <linux/platform_device.h>
> #include <linux/atmel_tc.h>
> +#include <linux/sched_clock.h>
>
>
> /*
> @@ -56,11 +57,16 @@ static u64 tc_get_cycles(struct clocksource *cs)
> return (upper << 16) | lower;
> }
>
> -static u64 tc_get_cycles32(struct clocksource *cs)
> +static u32 tc_get_cv32(void)
> {
> return __raw_readl(tcaddr + ATMEL_TC_REG(0, CV));
> }
>
> +static u64 tc_get_cycles32(struct clocksource *cs)
> +{
> + return tc_get_cv32();
> +}
> +
> static struct clocksource clksrc = {
> .name = "tcb_clksrc",
> .rating = 200,
> @@ -69,6 +75,11 @@ static struct clocksource clksrc = {
> .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> };
>
> +static u64 notrace tc_read_sched_clock(void)
> +{
> + return tc_get_cv32();
> +}
> +
> #ifdef CONFIG_GENERIC_CLOCKEVENTS
>
> struct tc_clkevt_device {
> @@ -339,6 +350,9 @@ static int __init tcb_clksrc_init(void)
> clksrc.read = tc_get_cycles32;
> /* setup ony channel 0 */
> tcb_setup_single_chan(tc, best_divisor_idx);
> +
> + /* register sched_clock on chips with single 32 bit counter */
> + sched_clock_register(tc_read_sched_clock, 32, divided_rate);
> } else {
> /* tclib will give us three clocks no matter what the
> * underlying platform supports.
>
--
Nicolas Ferre
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