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Date:   Mon, 7 Nov 2022 16:14:32 -0800
From:   Nicolin Chen <nicolinc@nvidia.com>
To:     Will Deacon <will@kernel.org>
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Subject: Re: [PATCH v7 4/5] iommu: Use EINVAL for incompatible device/domain
 in ->attach_dev
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On Mon, Nov 07, 2022 at 03:26:45PM +0000, Will Deacon wrote:

> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > index ba47c73f5b8c..01fd7df16cb9 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -2430,23 +2430,14 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >                       goto out_unlock;
> >               }
> >       } else if (smmu_domain->smmu != smmu) {
> > -             dev_err(dev,
> > -                     "cannot attach to SMMU %s (upstream of %s)\n",
> > -                     dev_name(smmu_domain->smmu->dev),
> > -                     dev_name(smmu->dev));
> > -             ret = -ENXIO;
> > +             ret = -EINVAL;
> >               goto out_unlock;
> >       } else if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 &&
> >                  master->ssid_bits != smmu_domain->s1_cfg.s1cdmax) {
> > -             dev_err(dev,
> > -                     "cannot attach to incompatible domain (%u SSID bits != %u)\n",
> > -                     smmu_domain->s1_cfg.s1cdmax, master->ssid_bits);
> >               ret = -EINVAL;
> >               goto out_unlock;
> >       } else if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 &&
> >                  smmu_domain->stall_enabled != master->stall_enabled) {
> > -             dev_err(dev, "cannot attach to stall-%s domain\n",
> > -                     smmu_domain->stall_enabled ? "enabled" : "disabled");
> >               ret = -EINVAL;
> >               goto out_unlock;
> >       }

> I think it would be helpful to preserve these messages using
> dev_err_ratelimited() so that attach failure can be diagnosed without
> having to hack the messages back into the driver.

Thank you for the review.

The change is already picked up last week. Yet, I can add prints
back with a followup patch, if no one has a problem with that.

Also, I am not quite sure what the use case would be to have an
error print. Perhaps dev_dbg() would be more fitting if it is
just for diagnosis?

Thanks
Nic