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

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Message-ID: <aK3eHkf31uIw04EH@lizhi-Precision-Tower-5810>
Date: Tue, 26 Aug 2025 12:17:34 -0400
From: Frank Li <Frank.li@....com>
To: Stanley Chu <stanley.chuys@...il.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 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.

>
> 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.

Only concern here is that svc_i3c_master_ack_ibi() need send in 100us by
i3c spec requirement.

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
>