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

[Bjorn Helgaas]

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@xxxxxxx>

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.