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

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Jun 08, 2021 at 09:11:27PM +0100, Jon Hunter wrote:
> On 08/06/2021 19:34, Vidya Sagar wrote:
> 
> ...
> 
> >>> 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?
> > Although it is the same driver that works for both HOST mode and EP
> > mode, PCIE_TEGRA194_EP depends on PCI_ENDPOINT whereas the
> > PCIE_TEGRA194_HOST mode doesn't. Similarly the PCIE_TEGRA194_HOST mode
> > depends on PCI_MSI_IRQ_DOMAIN which PCIE_TEGRA194_EP doesn't depend on.
> > It is possible to have end point mode support disabled (at sub-system
> > level) in the system yet pcie-tegra194 can be compiled for the host mode
> > vice-a-versa for the endpoint mode.
> > Hence, appropriate config HOST/EP needs to be selected to make sure that
> > the rest of the dependencies are enabled in the system.
> > Hope I'm able to give the rationale correctly here.
> 
> Yes but should we combine them like this ...
> 
> diff --git a/drivers/pci/controller/dwc/Kconfig b/drivers/pci/controller/dwc/Kconfig
> index 423d35872ce4..206455a9b70d 100644
> --- a/drivers/pci/controller/dwc/Kconfig
> +++ b/drivers/pci/controller/dwc/Kconfig
> @@ -254,15 +254,12 @@ config PCI_MESON
>           implement the driver.
>  
>  config PCIE_TEGRA194
> -       tristate
> -
> -config PCIE_TEGRA194_HOST
> -       tristate "NVIDIA Tegra194 (and later) PCIe controller - Host Mode"
> +       tristate "NVIDIA Tegra194 (and later) PCIe controller"
>         depends on ARCH_TEGRA_194_SOC || COMPILE_TEST
> -       depends on PCI_MSI_IRQ_DOMAIN
> -       select PCIE_DW_HOST
> +       depends on PCI_MSI_IRQ_DOMAIN || PCI_ENDPOINT
> +       select PCIE_DW_HOST if PCI_MSI_IRQ_DOMAIN
> +       select PCIE_DW_EP if PCI_ENDPOINT
>         select PHY_TEGRA194_P2U
> -       select PCIE_TEGRA194
>         help
>           Enables support for the PCIe controller in the NVIDIA Tegra194 SoC to
>           work in host mode. There are two instances of PCIe controllers in
> @@ -271,21 +268,6 @@ config PCIE_TEGRA194_HOST
>           in order to enable device-specific features PCIE_TEGRA194_EP must be
>           selected. This uses the DesignWare core.
>  
> -config PCIE_TEGRA194_EP
> -       tristate "NVIDIA Tegra194 (and later) PCIe controller - Endpoint Mode"
> -       depends on ARCH_TEGRA_194_SOC || COMPILE_TEST
> -       depends on PCI_ENDPOINT
> -       select PCIE_DW_EP
> -       select PHY_TEGRA194_P2U
> -       select PCIE_TEGRA194
> -       help
> -         Enables support for the PCIe controller in the NVIDIA Tegra194 SoC to
> -         work in endpoint mode. There are two instances of PCIe controllers in
> -         Tegra194. This controller can work either as EP or RC. In order to
> -         enable host-specific features PCIE_TEGRA194_HOST must be selected and
> -         in order to enable device-specific features PCIE_TEGRA194_EP must be
> -         selected. This uses the DesignWare core.

I'm not a Kconfig expert, but I really like that solution, as long as
it addresses Vidya's concerns about RP/EP dependencies.

Looks like the Kconfig help text should be updated to remove the
other PCIE_TEGRA194_EP reference?  Maybe it should include a clue
about how the connections to host/endpoint support, e.g., "includes
endpoint support if PCI_ENDPOINT is enabled"?

> Furthermore, I wonder if we should just move the code
> that is required for ACPI into it's own file like
> drivers/pci/controller/dwc/pcie-tegra194-acpi.c?

That might simplify things.  I think the reason we started with things
in one file is because for some drivers there's a lot of shared stuff
(#defines, register accessors) between the quirk and the native host
driver.  Either you have to put it all in one file, or you have to add
a shared .h file and make some of that stuff non-static.

Bjorn