linux-kernel - [PATCH] clocksource: timer-atmel-pit: don't suspend/resume if unused

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Date:	Thu, 18 Dec 2014 15:05:23 +0100
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	<daniel.lezcano@...aro.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	<sylvain.rochet@...secur.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: [PATCH] clocksource: timer-atmel-pit: don't suspend/resume if unused

From: Sylvain Rochet <sylvain.rochet@...secur.com>

Waiting for PIT to stop counting takes a long time:
  1/(Master clock/prescaler/PIVR)
= 1/(133 MHz     /16       /2^20)
= 126 ms

Up to 126 ms if master clock is set to 133 MHz, skipping suspend/resume
of the unused PIT device reduce (suspend time + resume time) from ~140 ms
to ~17 ms.

Signed-off-by: Sylvain Rochet <sylvain.rochet@...secur.com>
[nicolas.ferre@...el.com: move to newer clocksource driver]
Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
---
Hi Sylvain,

I re-worked (and "Acked") your patch so it can be applied on the newer Mainline
kernels. Beware, I changed the "subject line" as well. The PIT driver moved
recently (3.18).

Daniel,
Can you take this patch in your tree?

Thanks, bye.
  Nicolas.

 drivers/clocksource/timer-atmel-pit.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/clocksource/timer-atmel-pit.c b/drivers/clocksource/timer-atmel-pit.c
index b5b4d4585c9a..5408bc7c68d8 100644
--- a/drivers/clocksource/timer-atmel-pit.c
+++ b/drivers/clocksource/timer-atmel-pit.c
@@ -123,6 +123,10 @@ static void at91sam926x_pit_suspend(struct clock_event_device *cedev)
 {
 	struct pit_data *data = clkevt_to_pit_data(cedev);
 
+	/* Don't suspend PIT if unused */
+	if (cedev->mode == CLOCK_EVT_MODE_UNUSED)
+		return;
+
 	/* Disable timer */
 	pit_write(data->base, AT91_PIT_MR, 0);
 }
@@ -145,6 +149,10 @@ static void at91sam926x_pit_resume(struct clock_event_device *cedev)
 {
 	struct pit_data *data = clkevt_to_pit_data(cedev);
 
+	/* Don't resume PIT if unused */
+	if (cedev->mode == CLOCK_EVT_MODE_UNUSED)
+		return;
+
 	at91sam926x_pit_reset(data);
 }
 
-- 
2.1.3

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