linux-kernel - Re: [PATCH v3 09/11] i3c: master: svc: use spinlock_saveirq at svc_i3c_master_ibi

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Message-ID: <Zsi+ckEN/5Lt4fOS@lizhi-Precision-Tower-5810>
Date: Fri, 23 Aug 2024 12:53:06 -0400
From: Frank Li <Frank.li@....com>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Boris Brezillon <boris.brezillon@...labora.com>,
	Parshuram Thombare <pthombar@...ence.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Boris Brezillon <bbrezillon@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Conor Culhane <conor.culhane@...vaco.com>,
	linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org,
	imx@...ts.linux.dev
Subject: Re: [PATCH v3 09/11] i3c: master: svc: use spinlock_saveirq at
 svc_i3c_master_ibi_work()

On Fri, Aug 23, 2024 at 06:19:27PM +0200, Miquel Raynal wrote:
> Hi Frank,
>
> Frank.Li@....com wrote on Mon, 19 Aug 2024 12:02:03 -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 I3C/I2C Transfer,
>
> 				    low				    transfer
>
> > ACK/NACK Phase. But maximum stall time is 100us. We have to disable irq and
>
> and/or (I'm not sure)				the IRQs
>
> > schedule during whole I3C transaction, otherwise, I3C bus timeout will
>
> prevnet scheduling during the whole 		the      may
> timeout.
>
> > happen if any irq or schedule happen during transaction.
> >
> > Replace mutex with spinlock_saveirq() to make sure finish whole i3c
>
> 			wrong name	to avoid stalling SCL...
>
> > transaction without stall SCL more than 100us.
> >
> > Signed-off-by: Frank Li <Frank.Li@....com>
>
> Yes, 100us is low, and that's why I initially did my best to enforce
> auto ack/nack. We cannot make sure this limit will not be crossed, and
> when it's the case, we need to handle the consequences.

Only IBI use auto ack/nack. hardware can't handle it for HJ and CR, which
have to manually send out.


>
> > ---
> >  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 161ccd824443b..fbb6cef405577 100644
> > --- a/drivers/i3c/master/svc-i3c-master.c
> > +++ b/drivers/i3c/master/svc-i3c-master.c
> > @@ -432,7 +432,16 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
> >  	u32 status, val;
> >  	int ret;
> >
> > -	mutex_lock(&master->lock);
>
> Don't you still need this lock for other concurrency reasons?
>
> > +	/*
> > +	 * 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 I3C/I2C Transfer, ACK/NACK
> > +	 * Phase. But maximum stall time is 100us. We have to disable irq and schedule during whole
> > +	 * I3C transaction, otherwise, I3C bus timeout will happen if any irq or schedule happen
> > +	 * between 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,
> > @@ -452,7 +461,7 @@ 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);
>
> This means you lock one CPU for 100us doing nothing every time you send
> a frame, that's not possible. Actually the delay was already very small
> (could have been set to ~10 maybe) but this is not possible.

It happen only at error case. Most time should wait for only 9th SCL.
I think original comment is wrong.

Hardware set IBIWON at 8th SCL.

Frank

>
> >  	if (ret) {
> >  		dev_err(master->dev, "Timeout when polling for IBIWON\n");
> > @@ -525,7 +534,6 @@ 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)
> >
>
>
> Thanks,
> Miquèl