Re: [PATCH 3/5] PCI: cadence: Add host driver for Cadence PCIe controller

Lorenzo Pieralisi
2017-11-30T10:05:56Z

On Wed, Nov 29, 2017 at 06:25:15PM +0000, Lorenzo Pieralisi wrote:

[...]

> static void __iomem *cdns_pci_map_bus(struct pci_bus *bus, unsigned int devfn,
> int where)
>
> > +cdns_pci_map_bus(struct pci_bus *bus, unsigned int devfn, int where)
> > +{
> > + struct pci_host_bridge *bridge = pci_find_host_bridge(bus);
> > + struct cdns_pcie_rc *rc = pci_host_bridge_priv(bridge);
> > + struct cdns_pcie *pcie = &rc->pcie;
> > + unsigned int busn = bus->number;
> > + u32 addr0, desc0;
> > +
> > + if (busn < rc->bus_range->start || busn > rc->bus_range->end)
> > + return NULL;
>
> It does not hurt but I wonder whether you really need this check.
>
> > + if (busn == rc->bus_range->start) {
> > + if (devfn)
>
> I suspect I know why you need this check but I ask you to explain it
> anyway if you do not mind please.
>
> > + return NULL;
> > +
> > + return pcie->reg_base + (where & 0xfff);
> > + }
> > +
> > + /* Update Output registers for AXI region 0. */
> > + addr0 = CDNS_PCIE_AT_OB_REGION_PCI_ADDR0_NBITS(12) |
>
> Ok, so for every config access you reprogram addr0 to reflect the
> correct bus|devfn ID in the PCI bus TLP corresponding to an ECAM address
> in CPU physical address space, is my understanding correct ?

By re-reading it, it looks like this mechanism is there to just
associate a different RID TLP on the PCI bus to a fixed window
in CPU virtual address space.

> > + CDNS_PCIE_AT_OB_REGION_PCI_ADDR0_DEVFN(devfn) |
> > + CDNS_PCIE_AT_OB_REGION_PCI_ADDR0_BUS(busn);
> > + cdns_pcie_writel(pcie, CDNS_PCIE_AT_OB_REGION_PCI_ADDR0(0), addr0);
> > +
> > + /* Configuration Type 0 or Type 1 access. */
> > + desc0 = CDNS_PCIE_AT_OB_REGION_DESC0_HARDCODED_RID |
> > + CDNS_PCIE_AT_OB_REGION_DESC0_DEVFN(0);
> > + /*
> > + * The bus number was already set once for all in desc1 by
> > + * cdns_pcie_host_init_address_translation().
> > + */
> > + if (busn == rc->bus_range->start + 1)
> > + desc0 |= CDNS_PCIE_AT_OB_REGION_DESC0_TYPE_CONF_TYPE0;
> > + else
> > + desc0 |= CDNS_PCIE_AT_OB_REGION_DESC0_TYPE_CONF_TYPE1;
>
> I would like to ask you why you have to do it here and the root port
> does not figure it out by itself, I do not have the datasheet so I am
> just asking for my own information.
>
> > + cdns_pcie_writel(pcie, CDNS_PCIE_AT_OB_REGION_DESC0(0), desc0);
> > +
> > + return rc->cfg_base + (where & 0xfff);
> > +}

[...]

> > +static int cdns_pcie_host_init(struct device *dev,
> > + struct list_head *resources,
> > + struct cdns_pcie_rc *rc)
> > +{
> > + struct resource *bus_range = NULL;
> > + int err;
> > +
> > + /* Parse our PCI ranges and request their resources */
> > + err = cdns_pcie_parse_request_of_pci_ranges(dev, resources, &bus_range);
> > + if (err)
> > + goto err_out;
>
> I think that the err_out path should be part of:
>
> cdns_pcie_parse_request_of_pci_ranges()
>
> implementation and here you would just return.

I take it back, what you are doing is cleaner and allows you to
have code freeing the resource list in one single place so you
can leave this as-is.

Thanks,
Lorenzo