Subject: [PATCH V6 1/7] ACPI: I/O Remapping Table (IORT) initial support

From: [email-masked] (Lorenzo Pieralisi)
Date: Wed, 15 Jun 2016 14:34:23 +0100

On Wed, Jun 15, 2016 at 09:19:54AM -0400, Sinan Kaya wrote:
> Hi Tomasz,
> 
> > +static acpi_status
> > +iort_match_node_callback(struct acpi_iort_node *node, void *context)
> > +{
> > +	case ACPI_IORT_NODE_PCI_ROOT_COMPLEX: {
> > +		struct acpi_iort_root_complex *pci_rc;
> > +		struct pci_bus *bus;
> > +
> > +		bus = to_pci_bus(dev);
> > +		pci_rc = (struct acpi_iort_root_complex *)node->node_data;
> > +
> > +		/*
> > +		 * It is assumed that PCI segment numbers maps one-to-one
> > +		 * with root complexes. Each segment number can represent only
> > +		 * one root complex.
> > +		 */
> > +		if (pci_rc->pci_segment_number == pci_domain_nr(bus))
> > +			return AE_OK;
> > +
> 
> There is problem with the find_dev_node and callback for PCIe here. It assumes
> a one-to-one relationship between an SMMU and root complex. 
> 
> Just checked with Charles offline to see if there is anything in the IORT spec that forces
> this. And, the answer was no. 
> 
> Pasting the IORT requirements for you below.
> 
> ?The IORT was intended to be flexible enough to define static RID to SID mappings, which should cover 
> the following configurations:
> -	Dedicated SMMU per RC
> -	Multiple RC?s per SMMU (as you described)
> -	Multiple SMMU?s per RC (with static RID:SID range per SMMU)
> 
> The SMMU instance must be identified by either a device ID *or* a combination of 
> segment ID *and* Requestor ID. ?
> 
> If a root complex has multiple SMMUs, this code is going to return the
> first SMMU. This needs to be corrected.

What you say above is correct, but the problem is not here. This
callback returns either a named component IORT node or a root complex
IORT node corresponding to a device, the problem you are referring to is
related to detecting which SMMU a given named component or root
complex refers too, which is not done here, I will take care of that
on my SMMU series.

When we look for the SMMU a PCI device is connected to, we must first
retrieve the IORT node of its root complex and walk its list of
mappings and match through RID range instead of picking the first
one, as I assumed, wrongly.

Lorenzo

> 
> > +		break;
> > +	}
> > +	}
> > +
> > +	return AE_NOT_FOUND;
> > +}
> > +
> 
> > +
> > +static struct acpi_iort_node *
> > +iort_find_dev_node(struct device *dev)
> > +{
> > +	struct pci_bus *pbus;
> > +
> > +	if (!dev_is_pci(dev))
> > +		return iort_scan_node(ACPI_IORT_NODE_NAMED_COMPONENT,
> > +				      iort_match_node_callback, dev);
> > +
> > +	/* Find a PCI root bus */
> > +	pbus = to_pci_dev(dev)->bus;
> > +	while (!pci_is_root_bus(pbus))
> > +		pbus = pbus->parent;
> > +
> > +	return iort_scan_node(ACPI_IORT_NODE_PCI_ROOT_COMPLEX,
> > +			      iort_match_node_callback, &pbus->dev);
> > +}
> > +
> 
> -- 
> Sinan Kaya
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>