Re: [PATCH V2] PCI: tegra: Fix building Tegra194 PCIe driver

[Jon Hunter <jonathanh@nvidia.com>]

On 08/06/2021 14:02, Bjorn Helgaas wrote:
> On Tue, Jun 08, 2021 at 08:44:49AM +0100, Jon Hunter wrote:
>> On 08/06/2021 00:50, Bjorn Helgaas wrote:
>>
>> ...
>>
>>> My understanding is that we want pcie-tegra194.c to be:
>>>
>>>   - Built into the kernel when CONFIG_PCIE_TEGRA194=m or =y and
>>>     CONFIG_ACPI=y and CONFIG_PCI_QUIRKS=y.  If we're using the ACPI
>>>     pci_root.c driver, we must have the MCFG quirk built-in, and this
>>>     case worked as I expected (this is on x86):
>>>
>>>       $ grep -E "CONFIG_(ACPI\>|PCI_QUIRKS|PCIE_TEGRA194)" .config
>>>       CONFIG_ACPI=y
>>>       CONFIG_PCI_QUIRKS=y
>>>       CONFIG_PCIE_TEGRA194=y
>>>       CONFIG_PCIE_TEGRA194_HOST=m
>>>       CONFIG_PCIE_TEGRA194_EP=y
>>>
>>>       $ rm drivers/pci/controller/dwc/pcie-tegra194.*o
>>>       $ make drivers/pci/controller/dwc/
>>> 	...
>>> 	CC      drivers/pci/controller/dwc/pcie-tegra194.o
>>> 	AR      drivers/pci/controller/dwc/built-in.a
>>>
>>>   - Built as a module when CONFIG_PCIE_TEGRA194=m and CONFIG_ACPI is
>>>     not set.  In this case, we're not using the ACPI pci_root.c
>>>     driver, and we don't need the MCFG quirk built-in, so it should be
>>>     OK to build a module, and IIUC this patch is supposed to *allow*
>>>     that.  But in my testing, it did *not* build a module.  Am I
>>>     missing something?
>>>
>>>       $ grep -E "CONFIG_(ACPI\>|PCI_QUIRKS|PCIE_TEGRA194)" .config
>>>       # CONFIG_ACPI is not set
>>>       # CONFIG_PCI_QUIRKS is not set
>>>       CONFIG_PCIE_TEGRA194=y
>>>       CONFIG_PCIE_TEGRA194_HOST=m
>>>       CONFIG_PCIE_TEGRA194_EP=y
>>
>> The problem appears to be that you still have CONFIG_PCIE_TEGRA194=y and
>> CONFIG_PCIE_TEGRA194_EP=y above. If I have ...
> 
> Huh.  I can't set CONFIG_PCIE_TEGRA194 directly; it's only selectable
> by PCIE_TEGRA194_HOST and PCIE_TEGRA194_EP.  PCIE_TEGRA194 is
> tristate, but apparently kconfig sets it to the most restrictive,
> which I guess makes sense.
> 
> So I would expect the shared infrastructure to be built-in if either
> driver is built-in, but it's somewhat confusing that
> CONFIG_PCIE_TEGRA194_HOST=m results in a builtin driver.  If I can set
> CONFIG_PCIE_TEGRA194_HOST and CONFIG_PCIE_TEGRA194_EP independently,
> it seems like they should *be* independent.
> 
> What is the purpose of PCIE_TEGRA194_EP (added by c57247f940e8 ("PCI:
> tegra: Add support for PCIe endpoint mode in Tegra194") [1])?  I don't
> see any reference to it in a makefile or a source file.
> 
> It looks like one can build a single driver that works in either host
> or endpoint mode, depending on whether a DT node matches
> "nvidia,tegra194-pcie" or "nvidia,tegra194-pcie-ep".
> 
> So I think PCIE_TEGRA194_EP is superfluous and should be removed and
> you should have a single tristate Kconfig option.

This is a good point.

Sagar, any reason for this?

Jon
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