Re: [PATCH v4 1/2] PCI: pci-host-generic: add support for Synopsys DesignWare RC in ECAM mode

[Will Deacon <will.deacon@arm.com>]

On Tue, Oct 10, 2017 at 10:04:03AM +0100, Ard Biesheuvel wrote:
> On 10 October 2017 at 01:13, Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Mon, Oct 09, 2017 at 05:46:07PM +0100, Will Deacon wrote:
> >> On Fri, Oct 06, 2017 at 06:21:59PM -0500, Bjorn Helgaas wrote:
> >> > On Fri, Oct 06, 2017 at 05:39:18PM +0100, Ard Biesheuvel wrote:
> >> > > diff --git a/drivers/pci/host/pci-host-generic.c b/drivers/pci/host/pci-host-generic.c
> >> > > index 7d709a7e0aa8..01e81a30e303 100644
> >> > > --- a/drivers/pci/host/pci-host-generic.c
> >> > > +++ b/drivers/pci/host/pci-host-generic.c
> >> > > @@ -35,6 +35,43 @@ static struct pci_ecam_ops gen_pci_cfg_cam_bus_ops = {
> >> > >   }
> >> > >  };
> >> > >
> >> > > +static int pci_dw_ecam_config_read(struct pci_bus *bus, u32 devfn, int where,
> >> > > +                            int size, u32 *val)
> >> > > +{
> >> > > + struct pci_config_window *cfg = bus->sysdata;
> >> > > +
> >> > > + /*
> >> > > +  * The Synopsys DesignWare PCIe controller in ECAM mode will not filter
> >> > > +  * type 0 config TLPs sent to devices 1 and up on its downstream port,
> >> > > +  * resulting in devices appearing multiple times on bus 0 unless we
> >> > > +  * filter out those accesses here.
> >> > > +  */
> >> > > + if (bus->number == cfg->busr.start && PCI_SLOT(devfn) > 0)
> >> > > +         return PCIBIOS_DEVICE_NOT_FOUND;
> >> >
> >> > I think we should return 0xffffffff data here, as we do in other
> >> > similar accessors (dw_pcie_rd_conf(), altera_pcie_cfg_read(),
> >> > rockchip_pcie_rd_conf()).
> >> >
> >> > Actually, xilinx-nwl has a nice trick: it implements
> >> > nwl_pcie_map_bus(), which returns NULL for invalid devices.  Then it
> >> > can use the generic accessors, and pci_generic_config_read() already
> >> > fills in ~0 for this case.
> >> >
> >> > What do you think of the following?  I put it on my pci/host-generic
> >> > branch for now (pending your response and an ack from Will).
> >>
> >> I'd probably just inline the device check in pci_dw_ecam_map_bus directly,
> >> but either way:
> >>
> >> Acked-by: Will Deacon <will.deacon@arm.com>
> >
> > Thanks.  The reason I split out pci_dw_valid_device() is because there are
> > several other *_valid_device() functions in other drivers that do basically
> > the same thing, and I think it's useful to be able to see that they're all
> > similar, as opposed to being buried in the config accessor or map
> > functions, which vary a little more.
> >
> >> I'm assuming this is so small that there's no point in having a Kconfig
> >> option for these guys that depends on the generic host driver?
> >
> > Good question; I don't care either way.
> 
> In this case, may I suggest we leave the patch as is? Neither of you
> seem to mind, and it will make /my/ life much easier, given that I
> don't have to chase distros to get this driver enabled in their kernel
> configs (unless we make if 'def_bool y', in which case it makes even
> less sense to add the Kconfig option in the first place).

Yup, I acked it as-is, just thought it was worth asking the question.

Will