Re: [PATCH] i3c: renesas: Don't register devices when ENTDAA times out

From: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
To: Frank Li <Frank.li@oss.nxp.com>
Cc: tomm.merciai@gmail.com, linux-renesas-soc@vger.kernel.org,
	claudiu.beznea.uj@bp.renesas.com, biju.das.jz@bp.renesas.com,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Frank Li <Frank.Li@nxp.com>,
	linux-i3c@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] i3c: renesas: Don't register devices when ENTDAA times out
Date: Thu, 6 Aug 2026 11:30:53 +0200	[thread overview]
Message-ID: <anRUTcyZ0EZuctiR@tom-desktop> (raw)
In-Reply-To: <anOc3-M-ItT4mcPg@lizhi-Precision-Tower-5810>

Hi Frank,
Thanks for your review.

On Wed, Aug 05, 2026 at 04:28:15PM -0400, Frank Li wrote:
> On Fri, Jul 31, 2026 at 09:01:46AM +0200, Tommaso Merciai wrote:
> > renesas_i3c_daa() derives the number of newly assigned dynamic addresses
> > from cmd->rx_count, which the response ISR sets to the number of address
> > slots ENTDAA left unassigned. It starts out as zero, which already means
> > "every address was assigned", so a timed out transfer leaves that value
> > in place and it gets used as a result.
> >
> > On a bus with no target connected the ENTDAA times out and the driver
> > registers RENESAS_I3C_MAX_DEVS devices that are not there, each costing
> > the core two seconds on a GETPID that can only time out:
> >
> >   i3c i3c-0: Failed to add I3C device at address 9, error -110
> >   ...
> >   i3c i3c-0: Failed to add I3C device at address 16, error -110
> >
> > Start from maxdevs instead: no address is assigned before ENTDAA runs,
> > and the existing rx_count >= maxdevs check then reports an empty bus.
> >
> > Fixes: d028219a9f14 ("i3c: master: Add basic driver for the Renesas I3C controller")
> > Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
> > ---
> 
> Does https://lore.kernel.org/linux-i3c/alUZ_N9VdxkhcpqM@lizhi-Precision-Tower-5810/
> 
> fix the same problem?

[1] cover the case when ENTDAA completes and reports
rx_count == data_len == maxdevs,. 
This is what an empty bus looks like in the response descriptor.

This patch cover the case when ENTDAA never completes.
renesas_i3c_resp_isr() never run then cmd->rx_count = 0

then we will have:

	GENMASK(maxdevs - 0 - 1, 0)
	GENMASK(8 - 0 - 1, 0) = 0xff

This marks every free slot as newly assigned.

IMHO I think we are seeing the same issues but having different
causes.

[1] https://lore.kernel.org/linux-i3c/alUZ_N9VdxkhcpqM@lizhi-Precision-Tower-5810/

Kind regards,
Tommaso

> 
> Frank
> 
> >  drivers/i3c/master/renesas-i3c.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/i3c/master/renesas-i3c.c b/drivers/i3c/master/renesas-i3c.c
> > index 2b501f31e874..f4d9608978a9 100644
> > --- a/drivers/i3c/master/renesas-i3c.c
> > +++ b/drivers/i3c/master/renesas-i3c.c
> > @@ -685,7 +685,7 @@ static int renesas_i3c_daa(struct i3c_master_controller *m)
> >
> >  	init_completion(&xfer->comp);
> >  	cmd = xfer->cmds;
> > -	cmd->rx_count = 0;
> > +	cmd->rx_count = i3c->maxdevs;
> >
> >  	PM_RUNTIME_ACQUIRE_IF_ENABLED_AUTOSUSPEND(i3c->dev, pm);
> >  	ret = PM_RUNTIME_ACQUIRE_ERR(&pm);
> > --
> > 2.54.0
> >