Re: [PATCH 0/4] Loadable Module support for PCIe Cadence and J721E

On Wed, Mar 19, 2025 at 05:31:01PM +0800, Peter Chen wrote:

On 25-03-19 14:25:34, Siddharth Vadapalli wrote:

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Hello,

This series enables support to build the PCIe Cadence Controller drivers
and the PCI J721E Application/Wrapper/Glue driver as Loadable Kernel
Modules. The motivation for this series is that PCIe is not a necessity
for booting the SoC, due to which it doesn't have to be a built-in
module. Additionally, the defconfig doesn't enable the PCIe Cadence
Controller drivers and the PCI J721E driver, due to which PCIe is not
supported by default. Enabling the configs as of now (i.e. without this
series) will result in built-in drivers i.e. a bloated Linux Image for
everyone who doesn't have the PCIe Controller.

If the user doesn't enable PCIe controller device through DTS/ACPI,
that's doesn't matter.

The Linux Image for arm64 systems built using:
arch/arm64/configs/defconfig
will not have support for the Cadence PCIe Controller and the PCIe J721e
driver, because these configs aren't enabled.

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@@ -209,6 +209,12 @@ CONFIG_NFC=m
 CONFIG_NFC_NCI=m
 CONFIG_NFC_S3FWRN5_I2C=m
 CONFIG_PCI=y
+CONFIG_PCI_J721E=m
+CONFIG_PCI_J721E_HOST=m
+CONFIG_PCI_J721E_EP=m
+CONFIG_PCIE_CADENCE=m
+CONFIG_PCIE_CADENCE_HOST=m
+CONFIG_PCIE_CADENCE_EP=m

The common Cadence configuration will be select if the glue layer's
configuration is select according to Kconfig.

Please do not set common configuration as module, some user may need
it as build-in like dw's. Considering the situation, the rootfs is at
NVMe.

The common configuration at the moment is "DISABLED" i.e. no support for
the Cadence Controller at all. Which "user" are you referring to? This
series was introduced since having the drivers built-in was pushed back at:

We are using Cadence controller, and prepare upstream radxa-o6 board
whose rootfs is at PCIe NVMe.

It doesn't matter. Only criteria AFAIK to build the driver as built-in in
defconfig is that it should be a depedency for console. For some time, storage
was also a dependency, but for sure PCIe is not.

Moreover, CONFIG_BLK_DEV_NVME is built as a module in ARM64 defconfig. So it
doesn't matter if you build PCIe controller driver as a built-in or not. You
need to load the NVMe driver somehow.

So please use initramfs.

You could build driver as module for TI glue layer, but don't force
other vendors using module as well, see dwc as an example please.

DWC is a bad example here. Only reason the DWC drivers are not loadable is due
to the in-built MSI controller implementation as irqchip. People tend to build
the irqchip controllers as always built-in for some known issues. Even then some
driver developers prefer to built them as loadable module but suppress unbind to
avoid rmmoding the module.

- Mani

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