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

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Message-ID: <20250319062534.ollh3s5t7znf5zqs@uda0492258>
Date: Wed, 19 Mar 2025 11:55:34 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Peter Chen <peter.chen@...tech.com>
CC: Siddharth Vadapalli <s-vadapalli@...com>, <lpieralisi@...nel.org>,
        <kw@...ux.com>, <manivannan.sadhasivam@...aro.org>, <robh@...nel.org>,
        <bhelgaas@...gle.com>, <vigneshr@...com>, <kishon@...nel.org>,
        <cassel@...nel.org>, <wojciech.jasko-EXT@...tinental-corporation.com>,
        <thomas.richard@...tlin.com>, <bwawrzyn@...co.com>,
        <linux-pci@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <srk@...com>
Subject: Re: [PATCH 0/4] Loadable Module support for PCIe Cadence and J721E

On Wed, Mar 19, 2025 at 02:09:03PM +0800, Peter Chen wrote:

Hello Peter,

> On 25-03-07 16:01:24, Siddharth Vadapalli wrote:
> > EXTERNAL EMAIL
> >
> > 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.

> 
> > @@ -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:
https://lore.kernel.org/linux-arm-kernel/20250122145822.4ewsmkk6ztbeejzf@slashing/

Regards,
Siddharth.