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authorJisheng Zhang <jszhang@marvell.com>2015-11-05 10:32:06 +0800
committerDaniel Lezcano <daniel.lezcano@linaro.org>2015-12-15 09:42:00 +0100
commit9115df89d12c2cf6db080a7ee57cd076f8416e4a (patch)
treecfd86473d7034ace8133978e0f747d201b7125eb /drivers/clocksource
parent0901f18432db704b7622c969a09fba9846e4cfcd (diff)
clocksource/drivers/dw_apb_timer_of: Implement ARM delay timer
Implement an ARM delay timer to be used for udelay(). This allows us to skip the delay loop calibration at boot on Marvell BG2, BG2Q, BG2CD platforms. And after this patch, udelay() will be unaffected by CPU frequency changes. Note: Although in case there are several possible delay timers, we may not select the "best" delay timer. Take one Marvell Berlin platform for example: we have arch timer and dw-apb timer. The arch timer freq is 25MHZ while the dw-apb timer freq is 100MHZ, current selection would choose the dw-apb timer. But the dw apb timer is on the APB bus while arch timer sits in CPU, the cost of accessing the apb timer is higher than the arch timer. We could introduce "rating" concept to delay timer, but this approach "brings a lot of complexity and workarounds in the code for a small benefit" as pointed out by Daniel. Later, Arnd pointed out "However, we could argue that this actually doesn't matter at all, because the entire point of the ndelay()/ udelay()/mdelay() functions is to waste CPU cycles doing not much at all, so we can just as well waste them reading the timer register than spinning on the CPU reading the arch timer more often.", so we just simply register the dw apb base delay timer. Signed-off-by: Jisheng Zhang <jszhang@marvell.com> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Diffstat (limited to 'drivers/clocksource')
-rw-r--r--drivers/clocksource/dw_apb_timer_of.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/drivers/clocksource/dw_apb_timer_of.c b/drivers/clocksource/dw_apb_timer_of.c
index a19a3f619cc7..860843cef572 100644
--- a/drivers/clocksource/dw_apb_timer_of.c
+++ b/drivers/clocksource/dw_apb_timer_of.c
@@ -16,6 +16,7 @@
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
+#include <linux/delay.h>
#include <linux/dw_apb_timer.h>
#include <linux/of.h>
#include <linux/of_address.h>
@@ -130,6 +131,17 @@ static void __init init_sched_clock(void)
sched_clock_register(read_sched_clock, 32, sched_rate);
}
+#ifdef CONFIG_ARM
+static unsigned long dw_apb_delay_timer_read(void)
+{
+ return ~readl_relaxed(sched_io_base);
+}
+
+static struct delay_timer dw_apb_delay_timer = {
+ .read_current_timer = dw_apb_delay_timer_read,
+};
+#endif
+
static int num_called;
static void __init dw_apb_timer_init(struct device_node *timer)
{
@@ -142,6 +154,10 @@ static void __init dw_apb_timer_init(struct device_node *timer)
pr_debug("%s: found clocksource timer\n", __func__);
add_clocksource(timer);
init_sched_clock();
+#ifdef CONFIG_ARM
+ dw_apb_delay_timer.freq = sched_rate;
+ register_current_timer_delay(&dw_apb_delay_timer);
+#endif
break;
default:
break;