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

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Date:   Mon, 9 Oct 2017 17:46:07 +0100
From:   Will Deacon <will.deacon@....com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Leif Lindholm <leif.lindholm@...aro.org>,
        Graeme Gregory <graeme.gregory@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v4 1/2] PCI: pci-host-generic: add support for Synopsys
 DesignWare RC in ECAM mode

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@....com>

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?

Will