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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-i3c" Errors-To: linux-i3c-bounces+linux-i3c=archiver.kernel.org@lists.infradead.org On Mon, Apr 13, 2026 at 08:50:40AM +0800, Stanley Chu wrote: > From: Stanley Chu > > On NPCM845, when a target on the I3C bus gets stuck holding SDA low, > the controller reports a false Master Request (MR) in-band interrupt > event. The driver handles this by emitting a STOP condition to restore > the bus. > > However, the hardware quirk SVC_I3C_QUIRK_FALSE_SLVSTART indicates that > emitting a STOP condition may spuriously set the SLVSTART interrupt > status bit. In the Master Request case, this creates a feedback loop: > the STOP triggers a new SLVSTART event, the IRQ handler fires again, > the controller still reports an MR type, another STOP is emitted, and > the cycle repeats indefinitely, resulting in an IRQ storm that can lock > up the CPU. > > Clear the SLVSTART status bit explicitly after emitting the STOP in the > Master Request IBI handler when the SVC_I3C_QUIRK_FALSE_SLVSTART quirk > is set. This breaks the feedback loop without affecting normal SLVSTART > processing, which is already guarded in the top-level IRQ handler by > checking that MSTATUS is in SLVREQ state. > > Signed-off-by: Stanley Chu > --- Reviewed-by: Frank Li > drivers/i3c/master/svc-i3c-master.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c > index 7d88e8fe3742..c16397013334 100644 > --- a/drivers/i3c/master/svc-i3c-master.c > +++ b/drivers/i3c/master/svc-i3c-master.c > @@ -655,6 +655,15 @@ static void svc_i3c_master_ibi_isr(struct svc_i3c_master *master) > break; > case SVC_I3C_MSTATUS_IBITYPE_MASTER_REQUEST: > svc_i3c_master_emit_stop(master); > + > + /* > + * If a target gets stuck holding SDA low, the controller reports a MR. > + * On NPCM845, emitting STOP may spuriously set SLVSTART, retriggering > + * the interrupt and re-entering MR handling, leading to an IRQ storm. > + * Clear SLVSTART after STOP to break the loop. > + */ > + if (svc_has_quirk(master, SVC_I3C_QUIRK_FALSE_SLVSTART)) > + writel(SVC_I3C_MINT_SLVSTART, master->regs + SVC_I3C_MSTATUS); > break; > default: > break; > -- > 2.34.1 > -- linux-i3c mailing list linux-i3c@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-i3c