linux-kernel - Re: No controller seen in /sys/kernel/config/pci

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Message-ID: <ff345fdf-4398-0275-1e1d-f87e15b31d3a@ti.com>
Date:   Thu, 21 Jul 2022 16:02:53 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Ajay Garg <ajaygargnsit@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: No controller seen in /sys/kernel/config/pci_ep/controllers



On 21/07/22 15:54, Ajay Garg wrote:
> Any pointers please?
> 
> Thanks and Regards,
> Ajay
> 
> On Wed, Jul 13, 2022 at 11:48 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>
>> [+to Kishon, endpoint maintainer, +cc LKML]
>>
>> On Wed, Jul 13, 2022 at 12:53:06PM +0530, Ajay Garg wrote:
>>> Hello everyone.
>>>
>>> The kernel has been built with :
>>>
>>> ###################################
>>> CONFIG_PCI_ENDPOINT=y
>>> CONFIG_PCI_ENDPOINT_CONFIGFS=y
>>> CONFIG_PCI_EPF_TEST=y
>>> CONFIG_PCI_ENDPOINT_TEST=y
>>> ###################################
>>>
>>>
>>> Thereafter, following are seen :
>>>
>>> ###################################
>>> $ sudo mount none /sys/kernel/config/ -t configfs
>>> mount: /sys/kernel/config: none already mounted or mount point busy.
>>>
>>> $ ls -lrth /sys/class/pci_epc/
>>> total 0
>>>
>>> $ ls -lrth /sys/kernel/config
>>> total 0
>>> drwxr-xr-x 4 root root 0 Jul 13 10:58 pci_ep
>>> drwxr-xr-x 2 root root 0 Jul 13 10:58 usb_gadget
>>>
>>> $ ls -lrth /sys/kernel/config/pci_ep/functions
>>> total 0
>>> drwxr-xr-x 2 root root 0 Jul 13 10:58 pci_epf_test
>>>
>>> $ ls -lrth /sys/kernel/config/pci_ep/controllers
>>> total 0
>>>
>>> $
>>> ###################################
>>>
>>> What is being missed?
>>>
>>> Side Queries : Is the controller that is expected to be listed, a
>>> virtual-controller (like the one provided by CONFIG_USB_DUMMY_HCD in
>>> case of USB)?

There are no virtual PCIe endpoint controllers in Linux.
>>>
>>> Or there must be a real additional controller for pci-endpoint purpose?

right, there should be an endpoint controller and the driver for it
should register with the Linux endpoint framework.
>>> If yes, then :
>>>
>>>               * I guess no listing is expected currently, as my machine has just
>>>                 one controller (as pci-host).

correct.
>>>
>>>               * Is there a way to have an additional virtual pci-controller?

Not sure what exactly your use case is. All it's going to need is the
driver to use devm_pci_epc_create() to register a endpoint controller.

You can refer existing endpoint controller drivers
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/cadence/pcie-cadence-ep.c
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/dwc/pcie-designware-ep.c

Thanks,
Kishon