linux-kernel - Re: [PATCH v5 4/6] i3c: master: svc: use spin_lock_irqsave at svc_i3c_master_ibi

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Message-ID: <20241001221509.7d418d15@xps-13>
Date: Tue, 1 Oct 2024 22:15:09 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Frank Li <Frank.Li@....com>
Cc: Conor Culhane <conor.culhane@...vaco.com>, Alexandre Belloni
 <alexandre.belloni@...tlin.com>, linux-i3c@...ts.infradead.org,
 linux-kernel@...r.kernel.org, imx@...ts.linux.dev
Subject: Re: [PATCH v5 4/6] i3c: master: svc: use spin_lock_irqsave at
 svc_i3c_master_ibi_work()

Hi Frank,

Frank.Li@....com 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@....com>
> ---
> 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?

>  	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@...tlin.com>


Thanks,
Miquèl