[PATCH v1 1/2] i3c: master: svc: Fix missed IBI after false SLVSTART on NPCM845

[Frank Li]

On Mon, Apr 13, 2026 at 08:50:39AM +0800, Stanley Chu wrote:
> From: Stanley Chu <yschu at nuvoton.com>
>
> The NPCM845 I3C controller may raise a false SLVSTART interrupt. The
> handler first latches MSTATUS and then clears SLVSTART. If a real IBI
> request arrives after the handler latches MSTATUS but before it clears
> the SLVSTART interrupt status,

How this happen? If irq handler running, hardware (real IBI) will trigger
irq line before it.

Do you enable other type irq?

Frank

> HW sets the SLVREQ state. However, the
> handler still relies on the stale MSTATUS snapshot, returns early, and
> misses the real IBI. No further interrupt is generated for this pending
> IBI.
>
> Re-read MSTATUS to obtain the latest state and avoid missing a real IBI
> due to this race condition.
>
> Fixes: 4dd12e944f07 ("i3c: master: svc: Fix npcm845 invalid slvstart event")
> Signed-off-by: Stanley Chu <yschu at nuvoton.com>
> ---
>  drivers/i3c/master/svc-i3c-master.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> index b84b324e4111..7d88e8fe3742 100644
> --- a/drivers/i3c/master/svc-i3c-master.c
> +++ b/drivers/i3c/master/svc-i3c-master.c
> @@ -672,10 +672,18 @@ static irqreturn_t svc_i3c_master_irq_handler(int irq, void *dev_id)
>  	/* Clear the interrupt status */
>  	writel(SVC_I3C_MINT_SLVSTART, master->regs + SVC_I3C_MSTATUS);
>
> -	/* Ignore the false event */
> -	if (svc_has_quirk(master, SVC_I3C_QUIRK_FALSE_SLVSTART) &&
> -	    !SVC_I3C_MSTATUS_STATE_SLVREQ(active))
> -		return IRQ_HANDLED;
> +	if (svc_has_quirk(master, SVC_I3C_QUIRK_FALSE_SLVSTART)) {
> +		/*
> +		 * Re-read MSTATUS to obtain the latest state and avoid
> +		 * missing an IBI that arrives after MSTATUS is latched
> +		 * but before SLVSTART is cleared.
> +		 */
> +		active = readl(master->regs + SVC_I3C_MSTATUS);
> +
> +		/* Ignore the false event */
> +		if (!SVC_I3C_MSTATUS_STATE_SLVREQ(active))
> +			return IRQ_HANDLED;
> +	}
>
>  	/*
>  	 * The SDA line remains low until the request is processed.
> --
> 2.34.1
>