Re: [PATCH V4 4/7] ARM64, ACPI, PCI: I/O Remapping Table (IORT) initial support.

[Tomasz Nowicki]

On 13.04.2016 17:23, Marc Zyngier wrote:
> On 04/04/16 09:52, Tomasz Nowicki wrote:
> > IORT shows representation of IO topology for ARM based systems.
> > It describes how various components are connected together on
> > parent-child basis e.g. PCI RC -> SMMU -> ITS. Also see IORT spec.
> >
> > Initial support allows to:
> > - register ITS MSI chip along with ITS translation ID and domain token
> > - deregister ITS MSI chip based on ITS translation ID
> > - find registered domain token based on ITS translation ID
> > - map MSI RID based on PCI device and requester ID
> > - find domain token based on PCI device and requester ID
> >
> > To: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> > Signed-off-by: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> > ---
> >   drivers/acpi/Kconfig    |   3 +
> >   drivers/acpi/Makefile   |   1 +
> >   drivers/acpi/iort.c     | 335 ++++++++++++++++++++++++++++++++++++++++++++++++
> >   drivers/irqchip/Kconfig |   1 +
> >   include/linux/iort.h    |  31 +++++
> >   5 files changed, 371 insertions(+)
> >   create mode 100644 drivers/acpi/iort.c
> >   create mode 100644 include/linux/iort.h
>
> [...]
>
> > +static acpi_status
> > +iort_find_dev_callback(struct acpi_iort_node *node, void *context)
> > +{
> > +	struct acpi_iort_root_complex *pci_rc;
> > +	struct device *dev = context;
> > +	struct pci_bus *bus;
> > +
> > +	switch (node->type) {
> > +	case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> > +		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;
>
> What guarantees that this is ever valid? As far as I know, pci_domain_nr
> is completely arbitrary, and depends both on the probe order and the
> phase of the moon. If you want this to be reliable, you need to allocate
> the domain number from pci_segment_number.
>
> I must be missing something. Care to shed some light on this?
Sure. Please see:
http://infocenter.arm.com/help/topic/com.arm.doc.den0049a/DEN0049A_IO_Remapping_Table.pdf
3.1.1.5 PCI root complex node
PCI Segment number -> The PCI segment number, as in MCFG and as
returned by _SEG in the namespace.

So IORT spec states that pci_segment_number corresponds to the segment 
number from MCFG table and _SEG method. Here is my patch which makes 
sure pci_domain_nr(bus) is set properly:
https://lkml.org/lkml/2016/2/16/418

Tomasz