linux-kernel - Re: [PATCH 1/2] soc: fsl: qbman: qman_portal: defer probing when qman is not available

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Date:   Thu, 27 Sep 2018 14:24:48 -0500
From:   Li Yang <leoyang.li@....com>
To:     alexandre.belloni@...tlin.com,
        Laurentiu Tudor <laurentiu.tudor@....com>
Cc:     Olof Johansson <olof@...om.net>, Roy Pledge <roy.pledge@....com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] soc: fsl: qbman: qman_portal: defer probing when qman
 is not available

On Wed, Sep 26, 2018 at 1:15 PM Li Yang <leoyang.li@....com> wrote:
>
> On Wed, Sep 26, 2018 at 4:28 AM Alexandre Belloni
> <alexandre.belloni@...tlin.com> wrote:
> >
> > On 25/09/2018 21:45:56+0200, Olof Johansson wrote:
> > > Hi,
> > >
> > >
> > > On Thu, Aug 23, 2018 at 11:36 PM Alexandre Belloni
> > > <alexandre.belloni@...tlin.com> wrote:
> > > >
> > > > If the qman driver (qman_ccsr) doesn't probe or fail to probe before
> > > > qman_portal, qm_ccsr_start will be either NULL or a stale pointer to an
> > > > unmapped page.
> > > >
> > > > This leads to a crash when probing  qman_portal as the init_pcfg function
> > > > calls qman_liodn_fixup that tries to read qman registers.
> > > >
> > > > Assume that qman didn't probe when the pool mask is 0.
> > > >
> > > > Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> > > > ---
> > > >  drivers/soc/fsl/qbman/qman_portal.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/soc/fsl/qbman/qman_portal.c b/drivers/soc/fsl/qbman/qman_portal.c
> > > > index a120002b630e..4fc80d2c8feb 100644
> > > > --- a/drivers/soc/fsl/qbman/qman_portal.c
> > > > +++ b/drivers/soc/fsl/qbman/qman_portal.c
> > > > @@ -277,6 +277,8 @@ static int qman_portal_probe(struct platform_device *pdev)
> > > >         }
> > > >
> > > >         pcfg->pools = qm_get_pools_sdqcr();
> > > > +       if (pcfg->pools == 0)
> > > > +               return -EPROBE_DEFER;
> > >
> > > This is quite late in the probe, after a bunch of resources have been claimed.
> > >
> > > Note that the ioremaps above this are doing unwinds, and you'll end up
> > > doing duplicate ioremaps if you come in and probe again.
> > >
> > > You should probably unwind those allocations, or move them to devm_*
> > > or do this check earlier in the function.
> > >
> >
> > The actual chance of having that happen is quite small (this was coming
> > from a non working DT) and I mainly wanted to avoid a crash so the
> > platform could still boot. I would think moving to devm_ would be the
> > right thing to do.
>
> Even if it is not failing with the upstreamed device trees, it is
> still good to harden the driver for possible issues.  Moving to devm_
> is definitely a right thing to do.  But I also think checking if the
> qman is already probed should be the first thing to do before starting
> to allocate resources and etc and rolling back later.  Probably we can
> move the qm_get_pools_sdqcr() to the begining of the probe to
> determine if qman is probed as it doesn't seem to depend on any of the
> setups done right now.

I just find out Laurentiu also included the following patches in his
SMMU patch series (although not neccessarily related to SMMU) which
also fix the same problem.  I think they are more straightforward and
can deal with the case that qman failed to probe.  So we can take
these to fix this problem instead in 4.19.

https://patchwork.kernel.org/patch/10616021/
https://patchwork.kernel.org/patch/10616019/
https://patchwork.kernel.org/patch/10615971/

Regards,
Leo