[PATCH v5 3/6] iommu/arm-smmu-v3: Add feature detection for HTTU

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Nicolin Chen <nicolinc at nvidia.com>
> Sent: Friday, June 7, 2024 12:11 AM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi at huawei.com>
> Cc: iommu at lists.linux.dev; linux-arm-kernel at lists.infradead.org;
> robin.murphy at arm.com; will at kernel.org; joro at 8bytes.org;
> jgg at nvidia.com; ryan.roberts at arm.com; kevin.tian at intel.com;
> mshavit at google.com; eric.auger at redhat.com; joao.m.martins at oracle.com;
> jiangkunkun <jiangkunkun at huawei.com>; zhukeqian
> <zhukeqian1 at huawei.com>; Linuxarm <linuxarm at huawei.com>
> Subject: Re: [PATCH v5 3/6] iommu/arm-smmu-v3: Add feature detection for
> HTTU
> 
> Hi Shameer,
> 
> Some nitpicking inline.

Thanks for taking a look Nicolin.

> 
> On Thu, Jun 06, 2024 at 02:32:59PM +0100, Shameer Kolothum 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 e30ce55ed1af..c05a74aa52a4 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -3738,6 +3738,29 @@ static void arm_smmu_device_iidr_probe(struct
> arm_smmu_device *smmu)
> >         }
> >  }
> >
> > +static void arm_smmu_get_httu(struct arm_smmu_device *smmu, u32
> reg)
> 
> Following the other helper arm_smmu_device_iidr_probe, how about
> arm_smmu_device_httu_probe?

Hmm..I don't have any objection per se but "_get_" feels like more simple
and straightforward to me. Let me know if you feel strongly about this.
 
> And we could pass in FIELD_GET(IDR0_HTTU, reg) too?

Same here.

> 
> > +{
> > +       u32 fw_features = smmu->features & (ARM_SMMU_FEAT_HA |
> ARM_SMMU_FEAT_HD);
> > +       u32 httu = FIELD_GET(IDR0_HTTU, reg);
> > +       u32 features = 0;
> 
> How about "hw_feats" v.s. "fw_feats"?

Ok.

> 
> > +
> > +       switch (httu) {
> > +       case IDR0_HTTU_ACCESS_DIRTY:
> > +               features |= ARM_SMMU_FEAT_HD;
> > +               fallthrough;
> > +       case IDR0_HTTU_ACCESS:
> > +               features |= ARM_SMMU_FEAT_HA;
> > +       }
> > +
> > +       if (smmu->dev->of_node)
> > +               smmu->features |= features;
> > +       else if (features != fw_features)
> > +               /* ACPI IORT sets the HTTU bits */
> > +               dev_warn(smmu->dev,
> > +                        "IDR0.HTTU(0x%x) overridden by FW configuration
> (0x%x)\n",
> > +                         httu, fw_features);
> 
> httu and fw_features have different shifts -- could be odd to see:
> 	IDR0.HTTU(0x2) overridden by FW configuration (0x600000)
> 
> FIELD_GET(ACPI_IORT_SMMU_V3_HTTU_OVERRIDE, iort_smmu->flags)
> seems
> to be overcomplicated to reference? So, how about just features?
> +			"IDR0.HTTU features (0x%x) overridden by FW
> configuration (0x%x)\n",

Yes. I think that make sense. Will change.

Thanks,
Shameer