Re: [PATCH v3 8/8] iommu/arm-smmu-v3: Make default domain type of HiSilicon PTT device to identity

[John Garry]

On 08/02/2022 11:21, Yicong Yang wrote:
> > This patch should be earlier in the series, before the PTT driver, and the comment on hisi_ptt_check_iommu_mapping() should mention what is going on here.
> ok I'll reorder the serives and modify the comments of hisi_ptt_check_iommu_mapping() like:
>
> /*
>   * The DMA of PTT trace can only use direct mapping, due to some
>   * hardware restriction. Check whether there is an iommu or the
>   * policy of the iommu domain is passthrough, otherwise the trace
>   * cannot work.

IOMMU, capitalize acronyms

>   *
>   * The PTT device is supposed to behind the arm smmu v3, which
>   * should have passthrough the device by a quirk. Otherwise user
>   * should manually set the iommu domain type to identity through
>   * sysfs.

Sorry, but I don't really understand your meaning here.

I did not think that if we have a default domain then we can change via 
sysfs to anything else.

>   */
>
> > > Signed-off-by: Yicong Yang<yangyicong@xxxxxxxxxxxxx>
> > > ---
> > >    drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 16 ++++++++++++++++
> > >    1 file changed, 16 insertions(+)
> > >
> > > 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 6dc6d8b6b368..6f67a2b1dd27 100644
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > @@ -2838,6 +2838,21 @@ static int arm_smmu_dev_disable_feature(struct device *dev,
> > >        }
> > >    }
> > >    +#define IS_HISI_PTT_DEVICE(pdev)    ((pdev)->vendor == PCI_VENDOR_ID_HUAWEI && \
> > > +                     (pdev)->device == 0xa12e)
> > I assume that not all revisions will require this check, right?

So if you are very confident that the next revision will be fixed then I 
would add a check for this current broken revision.

> >
> For current revisions it's necessary.