Re: [PATCH v6 5/6] PCI: fu740: Add SiFive FU740 PCIe host controller driver

Bjorn Helgaas
2021-05-04T13:46:36Z

On Tue, May 04, 2021 at 06:59:39PM +0800, Greentime Hu wrote:
> From: Paul Walmsley <paul.walmsley@sifive.com>
>
> Add driver for the SiFive FU740 PCIe host controller.
> This controller is based on the DesignWare PCIe core.
>
> Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
> Co-developed-by: Henry Styles <hes@sifive.com>
> Signed-off-by: Henry Styles <hes@sifive.com>
> Co-developed-by: Erik Danie <erik.danie@sifive.com>
> Signed-off-by: Erik Danie <erik.danie@sifive.com>
> Co-developed-by: Greentime Hu <greentime.hu@sifive.com>
> Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
> ---
> drivers/pci/controller/dwc/Kconfig | 10 +
> drivers/pci/controller/dwc/Makefile | 1 +
> drivers/pci/controller/dwc/pcie-fu740.c | 309 ++++++++++++++++++++++++
> 3 files changed, 320 insertions(+)
> create mode 100644 drivers/pci/controller/dwc/pcie-fu740.c
>
> diff --git a/drivers/pci/controller/dwc/Kconfig b/drivers/pci/controller/dwc/Kconfig
> index 22c5529e9a65..255d43b1661b 100644
> --- a/drivers/pci/controller/dwc/Kconfig
> +++ b/drivers/pci/controller/dwc/Kconfig
> @@ -318,4 +318,14 @@ config PCIE_AL
> required only for DT-based platforms. ACPI platforms with the
> Annapurna Labs PCIe controller don't need to enable this.
>
> +config PCIE_FU740
> + bool "SiFive FU740 PCIe host controller"
> + depends on PCI_MSI_IRQ_DOMAIN
> + depends on SOC_SIFIVE || COMPILE_TEST
> + depends on GPIOLIB

1) I'm a little disappointed that I reported the build issue 6 days
ago when we were already in the merge window, and it's taken until
now to make some progress.

2) I would prefer not to depend on GPIOLIB because it reduces
compile-test coverage. For example, the x86_64 defconfig does not
enable GPIOLIB, so one must manually enable it to even be able to
enable PCIE_FU740.

Many other PCI controller drivers use GPIO, but no others depend on
GPIOLIB, so I infer that in the !GPIOLIB case, gpio/consumer.h
provides the stubs required for compile testing.

We could have a conversation about whether it's better to
explicitly depend on GPIOLIB here, or whether building a working
FU740 driver implicitly depends on GPIOLIB being selected
elsewhere. That implicit dependency *is* a little obscure, but I
think that's what other drivers currently do, and I'd like to do
this consistently unless there's a good reason otherwise.

Here are some examples of other drivers:

dwc/pci-dra7xx.c:
config PCI_DRA7XX_HOST
depends on SOC_DRA7XX || COMPILE_TEST

config SOC_DRA7XX
select ARCH_OMAP2PLUS

config ARCH_OMAP2PLUS
select GPIOLIB

dwc/pci-meson.c:
config PCI_MESON
# doesn't, but probably *should* depend on "ARCH_MESON || COMPILE_TEST"

menuconfig ARCH_MESON
select GPIOLIB

dwc/pcie-qcom.c:
config PCIE_QCOM
depends on OF && (ARCH_QCOM || COMPILE_TEST)

config ARCH_QCOM
select GPIOLIB

pcie-rockchip.c:
config PCIE_ROCKCHIP_HOST
depends on ARCH_ROCKCHIP || COMPILE_TEST

config ARCH_ROCKCHIP
select GPIOLIB

> + select PCIE_DW_HOST
> + help
> + Say Y here if you want PCIe controller support for the SiFive
> + FU740.
> +
> endmenu