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Message-ID: <20230830105211.07a2c790@xps-13>
Date: Wed, 30 Aug 2023 10:52:11 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Frank Li <Frank.li@....com>
Cc: Conor Culhane <conor.culhane@...vaco.com>,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
"moderated list:SILVACO I3C DUAL-ROLE MASTER"
<linux-i3c@...ts.infradead.org>,
open list <linux-kernel@...r.kernel.org>, imx@...ts.linux.dev
Subject: Re: [PATCH 2/2] i3c: master: svc: fix probe failure when no i3c
device exist
Hi Frank,
Frank.li@....com wrote on Tue, 29 Aug 2023 11:26:42 -0400:
> On Tue, Aug 29, 2023 at 11:16:11AM +0200, Miquel Raynal wrote:
> > Hi Frank,
> >
> > Frank.Li@....com wrote on Mon, 28 Aug 2023 15:25:02 -0400:
> >
> > > If there are not i3c device, all ccc command will get NACK. Set
> >
> > no NACKed?
> >
> > > i3c_ccc_cmd::err as I3C_ERROR_M2.
> >
> > This sentence should come last and be slightly more explicit.
> >
> > > Return success when no i3c device found at svc_i3c_master_do_daa_locked().
> >
> > Please explain why this is important/useful.
>
> If return failure, driver will probe failure when there are no any i3c
> devices. I3C master supposed support hot join. The probe failure don't
> make sense if no i3c devices found when master driver probe.
>
> How about rewrite commit log as
Much better, let me propose something slightly clearer.
> "I3C master supports device hot join, it doesn't make sense master driver
> probe failure when there are no I3C devices.
>
> When there are no I3C devices attached, all CCC commands are NACKed. So
> SVC I3C master fails to probe.
What about:
I3C masters are expected to support hot-join. This means at
initialization time we might not yet discover any device and this
should not be treated as a fatal error.
During the DAA procedure which happens at probe time, if no device has
joined, all CCC will be NACKed (from a bus perspective). This leads to
an early return with an error code which fails the probe of the master.
Let's avoid this by just telling the core through an I3C_ERROR_M2
return command code that no device was discovered, which is a valid
situation. This way the master will no longer bail out and fail to
probe for a wrong reason.
> Set i3c_cc_cmd:err as I3C_ERROR_M2. So I3C master framework
> i3c_master_rstdaa_locked() can return expected ERROR code and continue
> driver probe process.
>
> Return success at svc_i3c_master_do_daa_locked() if no i3c devices found.
> So SVC master driver can probe successfully even if no I3C devices are
> attached"
>
> >
> > > Fixes: dd3c52846d59 ("i3c: master: svc: Add Silvaco I3C master driver")
> >
> > Shall we consider a backport into stable kernels?
>
> Yes, I can add stable tag at next version.
Yes, please.
> >
> > > Signed-off-by: Frank Li <Frank.Li@....com>
> > > ---
> > > drivers/i3c/master/svc-i3c-master.c | 13 +++++++++++--
> > > 1 file changed, 11 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> > > index 770b40e28015e..a5620103acb73 100644
> > > --- a/drivers/i3c/master/svc-i3c-master.c
> > > +++ b/drivers/i3c/master/svc-i3c-master.c
> > > @@ -789,6 +789,9 @@ static int svc_i3c_master_do_daa_locked(struct svc_i3c_master *master,
> > > */
> > > break;
> > > } else if (SVC_I3C_MSTATUS_NACKED(reg)) {
> > > + /* No I3C devices attached */
> > > + if (dev_nb == 0)
> > > + break;
> >
> > \n ?
> >
> > > /*
> > > * A slave device nacked the address, this is
> > > * allowed only once, DAA will be stopped and
> > > @@ -1263,11 +1266,17 @@ static int svc_i3c_master_send_ccc_cmd(struct i3c_master_controller *m,
> > > {
> > > struct svc_i3c_master *master = to_svc_i3c_master(m);
> > > bool broadcast = cmd->id < 0x80;
> > > + int ret;
> > >
> > > if (broadcast)
> > > - return svc_i3c_master_send_bdcast_ccc_cmd(master, cmd);
> > > + ret = svc_i3c_master_send_bdcast_ccc_cmd(master, cmd);
> > > else
> > > - return svc_i3c_master_send_direct_ccc_cmd(master, cmd);
> > > + ret = svc_i3c_master_send_direct_ccc_cmd(master, cmd);
> > > +
> > > + if (ret)
> > > + cmd->err = I3C_ERROR_M2;
> > > +
> > > + return ret;
> > > }
> > >
> > > static int svc_i3c_master_priv_xfers(struct i3c_dev_desc *dev,
> >
> >
> > Thanks,
> > Miquèl
Thanks,
Miquèl
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