linux-kernel - Re: [PATCH v1] i3c: master: svc: Use manual response for IBI events

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Message-ID: <CAPwEoQPnxW2jRpcqE_QSW2rNm8-zHfkTF=Ns_w7szYj-k3bTXA@mail.gmail.com>
Date: Wed, 27 Aug 2025 08:54:03 +0800
From: Stanley Chu <stanley.chuys@...il.com>
To: Frank Li <Frank.li@....com>
Cc: miquel.raynal@...tlin.com, alexandre.belloni@...tlin.com, 
	linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	tomer.maimon@...oton.com, kwliu@...oton.com, yschu@...oton.com
Subject: Re: [PATCH v1] i3c: master: svc: Use manual response for IBI events

On Wed, Aug 27, 2025 at 12:17 AM Frank Li <Frank.li@....com> wrote:
>
> On Tue, Aug 19, 2025 at 05:08:31PM +0800, Stanley Chu wrote:
> > From: Stanley Chu <yschu@...oton.com>
> >
> > Using IBIRESP_AUTO causes the hardware to ACK IBI requests even when the
> > target is not in the device list. The svc_i3c_master_nack_ibi() has no
> > effect in such case.
>
> how this case can happen since default target's IBI is disabled. Need host
> send IBI enable command to target devices before target pull SDA lower.
>
Hi Frank,

This is to explain that the original code svc_i3c_master_nack_ibi()
will never take effect when using
AUTOIBI with IBIRESP_AUTO rule.
        /* Handle the critical responses to IBI's */
        switch (ibitype) {
        case SVC_I3C_MSTATUS_IBITYPE_IBI:
                dev = svc_i3c_master_dev_from_addr(master, ibiaddr);
                if (!dev || !is_events_enabled(master, SVC_I3C_EVENT_IBI)) {
                        svc_i3c_master_nack_ibi(master);
                }

> >
> > AutoIBI has another issue that the controller doesn't quit AutoIBI state
> > after an IBIWON polling timeout. The following sequence is the case:
> > 1. Target pulls SDA low
> > 2. SLVSTART interrupt triggers the IBI ISR
> > 3. Target releases SDA
> > 4. Driver writes AutoIBI request to MCTRL
> > 5. SDA is high, so AutoIBI process does not start
> > 6. IBIWON polling times out
> > 7. Controller state is AutoIBI and doesn't accept EmitStop request
> >
> > Emitting broadcast address with IBIRESP_MANUAL avoids both issues.
> >
> > Signed-off-by: Stanley Chu <yschu@...oton.com>
> > ---
> >  drivers/i3c/master/svc-i3c-master.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> > index 701ae165b25b..17644e041b44 100644
> > --- a/drivers/i3c/master/svc-i3c-master.c
> > +++ b/drivers/i3c/master/svc-i3c-master.c
> > @@ -517,9 +517,10 @@ static void svc_i3c_master_ibi_isr(struct svc_i3c_master *master)
> >        */
> >       writel(SVC_I3C_MINT_IBIWON, master->regs + SVC_I3C_MSTATUS);
> >
> > -     /* Acknowledge the incoming interrupt with the AUTOIBI mechanism */
> > -     writel(SVC_I3C_MCTRL_REQUEST_AUTO_IBI |
> > -            SVC_I3C_MCTRL_IBIRESP_AUTO,
> > +     /* Emit broadcast address for arbitration */
>
> Need comments here why Request_AutoIBI not work. I think it is IP design
> defect to make REQUEST_AUTO_IBI useless.
It is not an IP defect. Per spec, AutoIBI emits a START with address
7'h7E when a slave pulls SDA low.
A SDA glitch (high->low->high) can cause the controller to remain in
AutoIBI state.
1. SDA high->low: trigger IBI isr to execute
2. SDA low->high
3. IBI isr writes an AutoIBI request, the controller will not emit a
START because SDA is not low.
4. Finally IBIWON polling times out, the controller remains in AutoIBI state.

>
> Only concern here is that svc_i3c_master_ack_ibi() need send in 100us by
> i3c spec requirement.
The function svc_i3c_master_ack_ibi() executes promptly in the IRQ
handler, taking much less than 100 us.

---
Thanks.
Stanley
>
> Frank
>
> > +     writel(SVC_I3C_MCTRL_REQUEST_START_ADDR |
> > +            SVC_I3C_MCTRL_IBIRESP_MANUAL |
> > +            SVC_I3C_MCTRL_ADDR(I3C_BROADCAST_ADDR),
> >              master->regs + SVC_I3C_MCTRL);
> >
> >       /* Wait for IBIWON, should take approximately 100us */
> > @@ -539,10 +540,15 @@ static void svc_i3c_master_ibi_isr(struct svc_i3c_master *master)
> >       switch (ibitype) {
> >       case SVC_I3C_MSTATUS_IBITYPE_IBI:
> >               dev = svc_i3c_master_dev_from_addr(master, ibiaddr);
> > -             if (!dev || !is_events_enabled(master, SVC_I3C_EVENT_IBI))
> > +             if (!dev || !is_events_enabled(master, SVC_I3C_EVENT_IBI)) {
> >                       svc_i3c_master_nack_ibi(master);
> > -             else
> > +             } else {
> > +                     if (dev->info.bcr & I3C_BCR_IBI_PAYLOAD)
> > +                             svc_i3c_master_ack_ibi(master, true);
> > +                     else
> > +                             svc_i3c_master_ack_ibi(master, false);
> >                       svc_i3c_master_handle_ibi(master, dev);
> > +             }
> >               break;
> >       case SVC_I3C_MSTATUS_IBITYPE_HOT_JOIN:
> >               if (is_events_enabled(master, SVC_I3C_EVENT_HOTJOIN))
> > --
> > 2.34.1
> >