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

Fengquan Chen
2021-04-21T10:14:51Z

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

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/

>
> > Signed-off-by: Fengquan Chen <fengquan.chen@mediatek.com>
> > ---
> > 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.

>
> > 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)));
> >
> >