Re: [PATCH] clocksource: sh_cmt: Fix wrong setting if don't request IRQ for clock source channel

[Niklas Söderlund]

Hi Daniel,

On 2021-06-10 14:45:05 +0200, Daniel Lezcano wrote:
> On 22/04/2021 14:34, Niklas Söderlund wrote:
> > From: Phong Hoang <phong.hoang.wz@xxxxxxxxxxx>
> > 
> > If CMT instance has at least two channels, one channel will be used
> > as a clock source and another one used as a clock event device.
> > In that case, IRQ is not requested for clock source channel so
> > sh_cmt_clock_event_program_verify() might work incorrectly.
> > Besides, when a channel is only used for clock source, don't need to
> > re-set the next match_value since it should be maximum timeout as
> > it still is.
> > 
> > On the other hand, due to no IRQ, total_cycles is not counted up
> > when reaches compare match time (timer counter resets to zero),
> > so sh_cmt_clocksource_read() returns unexpected value.
> > Therefore, use 64-bit clocksoure's mask for 32-bit or 16-bit variants
> > will also lead to wrong delta calculation. Hence, this mask should
> > correspond to timer counter width, and above function just returns
> > the raw value of timer counter register.
> 
> I'm not getting the 'ch->cmt->num_channels == 1' change, can you explain?

My understanding is that if more then one channel is available the 
channel used as clocksource is used without an interrupt. This was not 
addressed in the patches listed as fixes. This patch fixes this multi 
channel use-case while still retaining the old behavior for for the case 
where only one channel is available (ch->cmt->num_channels == 
1).

> 
> > Fixes: bfa76bb12f23 ("clocksource: sh_cmt: Request IRQ for clock event device only")
> > Fixes: 37e7742c55ba ("clocksource/drivers/sh_cmt: Fix clocksource width for 32-bit machines")
> > Signed-off-by: Phong Hoang <phong.hoang.wz@xxxxxxxxxxx>
> > Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> > ---
> >  drivers/clocksource/sh_cmt.c | 30 ++++++++++++++++++------------
> >  1 file changed, 18 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/clocksource/sh_cmt.c b/drivers/clocksource/sh_cmt.c
> > index c98f8851fd680454..cadd09ad1a0946b9 100644
> > --- a/drivers/clocksource/sh_cmt.c
> > +++ b/drivers/clocksource/sh_cmt.c
> > @@ -578,7 +578,8 @@ static int sh_cmt_start(struct sh_cmt_channel *ch, unsigned long flag)
> >  	ch->flags |= flag;
> >  
> >  	/* setup timeout if no clockevent */
> > -	if ((flag == FLAG_CLOCKSOURCE) && (!(ch->flags & FLAG_CLOCKEVENT)))
> > +	if (ch->cmt->num_channels == 1 &&
> > +	    flag == FLAG_CLOCKSOURCE && (!(ch->flags & FLAG_CLOCKEVENT)))
> >  		__sh_cmt_set_next(ch, ch->max_match_value);
> >   out:
> >  	raw_spin_unlock_irqrestore(&ch->lock, flags);
> > @@ -620,20 +621,25 @@ static struct sh_cmt_channel *cs_to_sh_cmt(struct clocksource *cs)
> >  static u64 sh_cmt_clocksource_read(struct clocksource *cs)
> >  {
> >  	struct sh_cmt_channel *ch = cs_to_sh_cmt(cs);
> > -	unsigned long flags;
> >  	u32 has_wrapped;
> > -	u64 value;
> > -	u32 raw;
> >  
> > -	raw_spin_lock_irqsave(&ch->lock, flags);
> > -	value = ch->total_cycles;
> > -	raw = sh_cmt_get_counter(ch, &has_wrapped);
> > +	if (ch->cmt->num_channels == 1) {
> 
> 
> 
> > +		unsigned long flags;
> > +		u64 value;
> > +		u32 raw;
> >  
> > -	if (unlikely(has_wrapped))
> > -		raw += ch->match_value + 1;
> > -	raw_spin_unlock_irqrestore(&ch->lock, flags);
> > +		raw_spin_lock_irqsave(&ch->lock, flags);
> > +		value = ch->total_cycles;
> > +		raw = sh_cmt_get_counter(ch, &has_wrapped);
> >  
> > -	return value + raw;
> > +		if (unlikely(has_wrapped))
> > +			raw += ch->match_value + 1;
> > +		raw_spin_unlock_irqrestore(&ch->lock, flags);
> > +
> > +		return value + raw;
> > +	}
> > +
> > +	return sh_cmt_get_counter(ch, &has_wrapped);
> >  }
> >  
> >  static int sh_cmt_clocksource_enable(struct clocksource *cs)
> > @@ -696,7 +702,7 @@ static int sh_cmt_register_clocksource(struct sh_cmt_channel *ch,
> >  	cs->disable = sh_cmt_clocksource_disable;
> >  	cs->suspend = sh_cmt_clocksource_suspend;
> >  	cs->resume = sh_cmt_clocksource_resume;
> > -	cs->mask = CLOCKSOURCE_MASK(sizeof(u64) * 8);
> > +	cs->mask = CLOCKSOURCE_MASK(ch->cmt->info->width);
> >  	cs->flags = CLOCK_SOURCE_IS_CONTINUOUS;
> >  
> >  	dev_info(&ch->cmt->pdev->dev, "ch%u: used as clock source\n",
> > 
> 
> 
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-- 
Regards,
Niklas Söderlund