[PATCH] clocksource/drivers/timer-mediatek: optimize systimer irq clear flow on Mediatek Socs

clocksource/drivers/timer-mediatek: optimize systimer irq clear flow on Mediatek Socs

1)ensure systimer is enabled before clear and disable interrupt, which only
  for systimer in Mediatek Socs.

2)clear any pending timer-irq when shutdown to keep suspend flow clean,
  when use systimer as tick-broadcast timer

Signed-off-by: Fengquan Chen <redacted>

Fengquan Chen (1):
  clocksource/drivers/timer-mediatek: optimize systimer irq clear flow
    on Mediatek Socs

 drivers/clocksource/timer-mediatek.c | 4 ++++
 1 file changed, 4 insertions(+)

-- 
1.8.1.1.dirty
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1)ensure systimer is enabled before clear and disable interrupt, which only
for systimer in Mediatek Socs.

2)clear any pending timer-irq when shutdown to keep suspend flow clean,
when use systimer as tick-broadcast timer

Change-Id: Ia3eda83324af2fdaf5cbb3569a9bf020a11f8009
Signed-off-by: Fengquan Chen <redacted>
---
 drivers/clocksource/timer-mediatek.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
index 9318edc..9f1f095dc 100644
--- a/drivers/clocksource/timer-mediatek.c
+++ b/drivers/clocksource/timer-mediatek.c

@@ -75,6 +75,7 @@
 static void mtk_syst_ack_irq(struct timer_of *to)
 {
 	/* Clear and disable interrupt */
+	writel(SYST_CON_EN, SYST_CON_REG(to));
 	writel(SYST_CON_IRQ_CLR | SYST_CON_EN, SYST_CON_REG(to));
 }
 

@@ -111,6 +112,9 @@ static int mtk_syst_clkevt_next_event(unsigned long ticks,
 
 static int mtk_syst_clkevt_shutdown(struct clock_event_device *clkevt)
 {
+	/* Clear any irq */
+	mtk_syst_ack_irq(to_timer_of(clkevt));
+
 	/* Disable timer */
 	writel(0, SYST_CON_REG(to_timer_of(clkevt)));
 

-- 
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On 02/03/2021 08:28, Fengquan Chen wrote:

1)ensure systimer is enabled before clear and disable interrupt, which only
for systimer in Mediatek Socs.

2)clear any pending timer-irq when shutdown to keep suspend flow clean,
when use systimer as tick-broadcast timer

Change-Id: Ia3eda83324af2fdaf5cbb3569a9bf020a11f8009

Remove the above.

Add a Fixes tag.

	SYST_CON_EN is set below, why do you have to do it before?

Is that a hw bug ?

It is confusing what the description of the SYST_CON_EN says:

/*
 * SYST_CON_EN: Clock enable. Shall be set to
 *   - Start timer countdown.
 *   - Allow timeout ticks being updated.
 *   - Allow changing interrupt functions.

What means "interrupt functions" ?

Does writing writel(SYST_CON_EN, SYST_CON_REG(to)) before
SYST_CON_IRQ_CLR allows to clear the interrupt flag?

Can you explain how the timer works regarding this part?

It sounds to me a bit strange.

 *
 * SYST_CON_IRQ_EN: Set to allow interrupt.
 *
 * SYST_CON_IRQ_CLR: Set to clear interrupt.
 */

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On Thu, Mar 4, 2021 at 11:07 AM Fengquan Chen
[off-list ref] wrote:

1)ensure systimer is enabled before clear and disable interrupt, which only
for systimer in Mediatek Socs.

Why does the timer need to be enabled before the interrupt can be
disabled? The datasheet I have does not suggest that this is required.

This function seems to be mis-named. It does more than just ack the irq.

 {
        /* Clear and disable interrupt */
+       writel(SYST_CON_EN, SYST_CON_REG(to));

This line seems to enable the timer and disable the interrupt.

        writel(SYST_CON_IRQ_CLR | SYST_CON_EN, SYST_CON_REG(to));

This line acks the interrupt and enables the timer and disables the interrupt.
Are these lines both necessary?
Maybe this function should just ack the interrupt without changing the
other bits.

This is a third write to the same register, I believe all 3 writes can
be combined into 1. Is that possible?

--
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On Mon, 2021-03-22 at 11:10 +0100, Daniel Lezcano wrote:

On 02/03/2021 08:28, Fengquan Chen wrote:

quoted

1)ensure systimer is enabled before clear and disable interrupt, which only
for systimer in Mediatek Socs.

2)clear any pending timer-irq when shutdown to keep suspend flow clean,
when use systimer as tick-broadcast timer

Change-Id: Ia3eda83324af2fdaf5cbb3569a9bf020a11f8009

Remove the above.

Add a Fixes tag.

Thanks for review, has been fixed in V4:
https://patchwork.kernel.org/project/linux-mediatek/patch/1617960162-1988-2-git-send-email-Fengquan.Chen@mediatek.com/

quoted

Signed-off-by: Fengquan Chen <redacted>
---
 drivers/clocksource/timer-mediatek.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
index 9318edc..9f1f095dc 100644
--- a/drivers/clocksource/timer-mediatek.c
+++ b/drivers/clocksource/timer-mediatek.c

@@ -75,6 +75,7 @@
 static void mtk_syst_ack_irq(struct timer_of *to)
 {
 	/* Clear and disable interrupt */
+	writel(SYST_CON_EN, SYST_CON_REG(to));

	SYST_CON_EN is set below, why do you have to do it before?

Is that a hw bug ?

It is confusing what the description of the SYST_CON_EN says:

/*
 * SYST_CON_EN: Clock enable. Shall be set to
 *   - Start timer countdown.
 *   - Allow timeout ticks being updated.
 *   - Allow changing interrupt functions.

What means "interrupt functions" ?

Does writing writel(SYST_CON_EN, SYST_CON_REG(to)) before
SYST_CON_IRQ_CLR allows to clear the interrupt flag?

Can you explain how the timer works regarding this part?

It sounds to me a bit strange.

 *
 * SYST_CON_IRQ_EN: Set to allow interrupt.
 *
 * SYST_CON_IRQ_CLR: Set to clear interrupt.
 */

Thanks for review, descriptions about
SYST_CON_IRQ_CLR/SYST_CON_EN/SYST_CON_IRQ_EN have been updated in v4.

And for systimer, there's a hw limitation that before clearing pending
irqs, we must enable timer first. so we added a SYST_CON_EN write before
SYST_CON_IRQ_CLR write to ensure irq clear successfully.

Also, we cannot only write SYST_CON_IRQ_CLR without SYST_CON_EN bit,
because EN bit is also timer clock enable bit. 

this is a hardward design limitation but not a bug.

quoted

 	writel(SYST_CON_IRQ_CLR | SYST_CON_EN, SYST_CON_REG(to));
 }
 

@@ -111,6 +112,9 @@ static int mtk_syst_clkevt_next_event(unsigned long ticks,
 
 static int mtk_syst_clkevt_shutdown(struct clock_event_device *clkevt)
 {
+	/* Clear any irq */
+	mtk_syst_ack_irq(to_timer_of(clkevt));
+
 	/* Disable timer */
 	writel(0, SYST_CON_REG(to_timer_of(clkevt)));
 

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On Tue, 2021-03-23 at 11:48 +1100, Evan Benn wrote:

On Thu, Mar 4, 2021 at 11:07 AM Fengquan Chen
[off-list ref] wrote:

quoted

1)ensure systimer is enabled before clear and disable interrupt, which only
for systimer in Mediatek Socs.

Why does the timer need to be enabled before the interrupt can be
disabled? The datasheet I have does not suggest that this is required.

Thanks for review. For systimer, you must enable timer before clear
irq,it's a hw limitation that would be easily neglected.

quoted

2)clear any pending timer-irq when shutdown to keep suspend flow clean,
when use systimer as tick-broadcast timer

Change-Id: Ia3eda83324af2fdaf5cbb3569a9bf020a11f8009
Signed-off-by: Fengquan Chen <redacted>
---
 drivers/clocksource/timer-mediatek.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
index 9318edc..9f1f095dc 100644
--- a/drivers/clocksource/timer-mediatek.c
+++ b/drivers/clocksource/timer-mediatek.c

@@ -75,6 +75,7 @@
 static void mtk_syst_ack_irq(struct timer_of *to)

This function seems to be mis-named. It does more than just ack the irq.

quoted

 {
        /* Clear and disable interrupt */
+       writel(SYST_CON_EN, SYST_CON_REG(to));

This line seems to enable the timer and disable the interrupt.

quoted

        writel(SYST_CON_IRQ_CLR | SYST_CON_EN, SYST_CON_REG(to));

This line acks the interrupt and enables the timer and disables the interrupt.
Are these lines both necessary?
Maybe this function should just ack the interrupt without changing the
other bits.

Thanks for review. 

it's necessary.

As described above,we must enable timer before clear
irq, so here is just want to ensure irq clear successfully.

We always disable irq here, and will be re-enable in
mtk_syst_clkevt_next_event.

quoted

 }

@@ -111,6 +112,9 @@ static int mtk_syst_clkevt_next_event(unsigned long ticks,

 static int mtk_syst_clkevt_shutdown(struct clock_event_device *clkevt)
 {
+       /* Clear any irq */
+       mtk_syst_ack_irq(to_timer_of(clkevt));
+
        /* Disable timer */
        writel(0, SYST_CON_REG(to_timer_of(clkevt)));

This is a third write to the same register, I believe all 3 writes can
be combined into 1. Is that possible?

Thanks for review. 

there's a hw limitation here, we can not clear irq while timer is
disabled, and SYST_CON_EN&SYST_CON_IRQ_CLR bit must be write at the same
time or can not  write SYST_CON_IRQ_CLR bit seperately.

quoted

--
1.8.1.1.dirty

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