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

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Message-ID: <CAKv+Gu8_h=92bLpybsJytSb7p9_333iUTtXtSkDu19EJy0ws=A@mail.gmail.com>
Date:   Mon, 9 Oct 2017 19:50:04 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.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 9 October 2017 at 17:46, Will Deacon <will.deacon@....com> 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@....com>
>

Thanks

> 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?
>

I can make the compatible strings shorter if you like?