Re: [PATCH 2/2] iommu/arm-smmu-v3:Enable ACPI based HiSilicon erratum 161010801

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Jun 16, 2017 at 09:43:52AM +0000, Shameerali Kolothum Thodi wrote:
> Hi Lorenzo,
> 
> > -----Original Message-----
> > From: linuxarm-bounces@huawei.com [mailto:linuxarm-
> > bounces@huawei.com] On Behalf Of Shameerali Kolothum Thodi
> > Sent: Tuesday, June 13, 2017 3:53 PM
> > To: Lorenzo Pieralisi
> > Cc: marc.zyngier@arm.com; will.deacon@arm.com; Linuxarm; linux-
> > acpi@vger.kernel.org; iommu@lists.linux-foundation.org;
> > hanjun.guo@linaro.org; sudeep.holla@arm.com; robin.murphy@arm.com;
> > linux-arm-kernel@lists.infradead.org; devel@acpica.org
> > Subject: RE: [PATCH 2/2] iommu/arm-smmu-v3:Enable ACPI based HiSilicon
> > erratum 161010801
> 
> [...]
>  > > > ---
> > > >  drivers/iommu/arm-smmu-v3.c | 27 ++++++++++++++++++++++-----
> > > >  1 file changed, 22 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-
> > > v3.c
> > > > index abe4b88..2636c85 100644
> > > > --- a/drivers/iommu/arm-smmu-v3.c
> > > > +++ b/drivers/iommu/arm-smmu-v3.c
> > > > @@ -597,6 +597,7 @@ struct arm_smmu_device {
> > > >  	u32				features;
> > > >
> > > >  #define ARM_SMMU_OPT_SKIP_PREFETCH	(1 << 0)
> > > > +#define ARM_SMMU_OPT_RESV_HW_MSI	(1 << 1)
> > > >  	u32				options;
> > > >
> > > >  	struct arm_smmu_cmdq		cmdq;
> > > > @@ -1904,14 +1905,29 @@ static void
> > arm_smmu_get_resv_regions(struct
> > > device *dev,
> > > >  				      struct list_head *head)
> > > >  {
> > > >  	struct iommu_resv_region *region;
> > > > +	struct arm_smmu_device *smmu;
> > > > +	struct iommu_fwspec *fwspec = dev->iommu_fwspec;
> > > >  	int prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
> > > >
> > > > -	region = iommu_alloc_resv_region(MSI_IOVA_BASE,
> > > MSI_IOVA_LENGTH,
> > > > -					 prot, IOMMU_RESV_SW_MSI);
> > > > -	if (!region)
> > > > -		return;
> > > > +	smmu = arm_smmu_get_by_fwnode(fwspec->iommu_fwnode);
> > > >
> > > > -	list_add_tail(&region->list, head);
> > > > +	if (smmu && (smmu->options & ARM_SMMU_OPT_RESV_HW_MSI)
> > > &&
> > > > +		      dev_is_pci(dev)) {
> > > > +		int ret;
> > > > +
> > > > +		ret = iort_iommu_its_get_resv_regions(dev, head);
> > >
> > > This should be made fwnode dependent, it makes precious little sense to
> > call
> > > IORT to reserve regions on a DT based platforms (I know the
> > > ARM_SMMU_OPT_RESV_HW_MSI option is only selected in ACPI (?) but
> > > comment applies regardless - have you prototyped a DT version too ?).
> > 
> > Ok. I will add a check here. 
> 
> This is what I have in mind. Please take a look and let me know. I will send out
> a v2 of this series soon.
> ....
> if (smmu && (smmu->options & ARM_SMMU_OPT_RESV_HW_MSI) &&
> 			dev_is_pci(dev)) {
> 	int ret = -EINVAL;
> 
> 	if (!is_of_node(smmu->dev->fwnode))
> 		ret = iort_iommu_its_get_resv_regions(dev, head);
> 
> 	if (ret) {
> 		dev_warn(dev, "HW MSI region resv failed: %d\n", ret);
> 		return;
> 	}
> } else {

The fwnode handling is fine, I do not like much the:

dev_is_pci()

check because it relies on implicit knowledge of the platform and
the quirks you need (ie you know that it is _just_ a PCI RC quirk
implicitly), the logic behind reserving the regions is a bit
convoluted and not easy to understand at all.

Let me try to rephrase it: you know, through an SMMU model number,
that your PCI RC handles MSI in a specific way, but by reading the
code above this is not clear at all, at least to me. This is a PCI
RC quirk but it does not depend on any PCI RC specific firmware binding
whatsoever, that's what is a bit hard to understand.

Anyway you can post the patches and we will take it from there to
see if there is a way to improve it.

Thanks,
Lorenzo