On 28 September 2017 at 09:00, Will Deacon <will.deacon@xxxxxxx> wrote:
> On Thu, Sep 28, 2017 at 08:57:28AM -0700, Ard Biesheuvel wrote:
>> On 28 September 2017 at 02:03, Will Deacon <will.deacon@xxxxxxx> wrote:
>> > On Tue, Sep 26, 2017 at 12:32:00PM -0500, Bjorn Helgaas wrote:
>> >> [+cc Will]
>> >>
>> >> On Mon, Aug 28, 2017 at 07:04:36PM +0100, Ard Biesheuvel wrote:
>> >> > Some implementations of the Synopsys Designware PCIe controller implement
>> >> > a so-called ECAM shift mode, which allows a static memory window to be
>> >> > configured that covers the configuration space of the entire bus range.
>> >> >
>> >> > If the firmware performs all the low level configuration that is required
>> >> > to expose this controller in a fully ECAM compatible manner, we can
>> >> > simply describe it as "pci-host-ecam-generic" and be done with it.
>> >> > However, it appears that in some cases (one of which is the Armada 80x0),
>> >> > the IP is synthesized with an ATU window size that does not allow the
>> >> > first bus to be mapped in a way that prevents the device on the
>> >> > downstream port from appearing more than once.
>> >> >
>> >> > So implement a driver that relies on the firmware to perform all low
>> >> > level initialization, and drives the controller in ECAM mode, but
>> >> > overrides the config space accessors to take the above quirk into
>> >> > account.
>> >> >
>> >> > Note that, unlike most drivers for this IP, this driver does not expose
>> >> > a fake bridge device at B/D/F 00:00.0. There is no point in doing so,
>> >> > given that this is not a true bridge, and does not require any windows
>> >> > to be configured in order for the downstream device to operate correctly.
>> >> > Omitting it also prevents the PCI resource allocation routines from
>> >> > handing out BAR space to it unnecessarily.
>> >>
>> >> This is a tangent, but does this mean the other drivers do not need to
>> >> expose a fake 00:00.0 device either?
>> >>
>> >> s/Designware/DesignWare/ in comments, changelogs, Kconfig text, etc.
>> >>
>> >> > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> >> > Cc: Jingoo Han <jingoohan1@xxxxxxxxx>
>> >> > Cc: Joao Pinto <Joao.Pinto@xxxxxxxxxxxx>
>> >> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>> >> > ---
>> >> > drivers/pci/dwc/Kconfig | 11 +++
>> >> > drivers/pci/dwc/Makefile | 1 +
>> >> > drivers/pci/dwc/pcie-designware-ecam.c | 77 ++++++++++++++++++++
>> >>
>> >> This really doesn't have any DesignWare specifics in it, and it seems
>> >> more related to drivers/pci/host/pci-host-generic.c than to anything
>> >> in drivers/pci/dwc. Maybe it should be
>> >> drivers/pci/host/pci-host-generic-quirks.c or something? That's
>> >> unwieldy, I admit.
>> >>
>> >> Putting it in pci/dwc would make Jingoo and Joao the default
>> >> maintainers; I don't know how they feel about that. We would probably
>> >> have to tweak MAINTAINERS if we *didn't* put it in pci/dwc.
>> >>
>> >> Any thoughts on this, Will?
>> >
>> > The idea of a "generic quirk" makes me smile, I must admit :)
>> >
>> > I think there are two options:
>> >
>> > 1. Use the full DWC driver, and don't rely on firmware
>> > -or-
>> > 2. Rely on firmware, but teach pci-host-generic to deal with the funny
>> > config space
>> >
>> > For (2), we probably want to describe this as generically as possible
>> > in case some other SoCs run into the same problem.
>> >
>>
>> I take it this implies a DT property. I could add one that consists of
>> an array of val/mask tuples or base/size tuples that allow us to
>> disable arbitrary subregions of the config space. I could also add a
>> simple boolean property that implements this exact quirk. Do you have
>> any preference?
>
> I'd say either a boolean property or a new compatible string. I think Rob
> prefers the latter, from what he said recently on an SMMU thread.
>
OK. Given that Rob already acked the binding for this driver, I'll go
ahead and rework the patch to add
+ { .compatible = "marvell,armada8k-pcie-ecam" },
+ { .compatible = "socionext,synquacer-pcie-ecam" },
+ { .compatible = "snps,dw-pcie-ecam" },
to the pci-host-ecam-generic driver instead.
Thanks,
Ard.
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