Re: [PATCH v5 4/6] i3c: master: svc: use spin_lock_irqsave at svc_i3c_master_ibi_work()

[Frank Li]

On Tue, Oct 01, 2024 at 10:15:09PM +0200, Miquel Raynal wrote:
> Hi Frank,
>
> Frank.Li@xxxxxxx wrote on Tue, 01 Oct 2024 12:02:53 -0400:
>
> > According to I3C spec ver 1.1, 09-Jun-2021, section 5.1.2.5:
> >
> > The I3C Controller shall hold SCL low while the Bus is in ACK/NACK Phase of
> > I3C/I2C transfer. But maximum stall time is 100us. The IRQs have to be
> > disabled to prevent schedule during the whole I3C transaction, otherwise,
> > the I3C bus timeout may happen if any irq or schedule happen during
> > transaction.
> >
> > Replace mutex with spin_lock_irqsave() to avoid stalling SCL more than
> > 100us.
> >
> > Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> > ---
> > Change from v3-v4
> > - improve commit message
> > - needn't mutex here, other place already use spin_lock_saveirq to protent
> > i3c transfer.
> > ---
> >  drivers/i3c/master/svc-i3c-master.c | 14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> > index 5df0ec02d73ce..1ee6ce186195c 100644
> > --- a/drivers/i3c/master/svc-i3c-master.c
> > +++ b/drivers/i3c/master/svc-i3c-master.c
> > @@ -436,7 +436,16 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
> >  	u32 status, val;
> >  	int ret;
> >
> > -	mutex_lock(&master->lock);
> > +	/*
> > +	 * According to I3C spec ver 1.1, 09-Jun-2021, section 5.1.2.5:
> > +	 *
> > +	 * The I3C Controller shall hold SCL low while the Bus is in ACK/NACK Phase of I3C/I2C
> > +	 * transfer. But maximum stall time is 100us. The IRQs have to be disabled to prevent
> > +	 * schedule during the whole I3C transaction, otherwise, the I3C bus timeout may happen if
> > +	 * any irq or schedule happen during transaction.
> > +	 */
> > +	guard(spinlock_irqsave)(&master->xferqueue.lock);
> > +
> >  	/*
> >  	 * IBIWON may be set before SVC_I3C_MCTRL_REQUEST_AUTO_IBI, causing
> >  	 * readl_relaxed_poll_timeout() to return immediately. Consequently,
> > @@ -456,7 +465,7 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
> >  	       master->regs + SVC_I3C_MCTRL);
> >
> >  	/* Wait for IBIWON, should take approximately 100us */
> > -	ret = readl_relaxed_poll_timeout(master->regs + SVC_I3C_MSTATUS, val,
> > +	ret = readl_relaxed_poll_timeout_atomic(master->regs + SVC_I3C_MSTATUS, val,
> >  					 SVC_I3C_MSTATUS_IBIWON(val), 0, 1000);
>
> If we now are holding a spinlock and expect this to happen within
> 100us, then I guess the timeout should be reduced?

yes, 100 should be enough for timeout. Normal it should be set at 9th SCL.

Frank

>
> >  	if (ret) {
> >  		dev_err(master->dev, "Timeout when polling for IBIWON\n");
> > @@ -529,7 +538,6 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
> >
> >  reenable_ibis:
> >  	svc_i3c_master_enable_interrupts(master, SVC_I3C_MINT_SLVSTART);
> > -	mutex_unlock(&master->lock);
> >  }
> >
> >  static irqreturn_t svc_i3c_master_irq_handler(int irq, void *dev_id)
> >
>
> Otherwise,
>
> Reviewed-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
>
>
> Thanks,
> Miquèl
>
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