linux-kernel - Re: [PATCH v2 1/1] Guard pci_create_sysfs_dev

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Date:   Thu, 16 Mar 2023 15:01:25 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Alexander Stein <alexander.stein@...tq-group.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Oliver Neukum <oneukum@...e.com>
Cc:     Korneliusz Osmenda <korneliuszo@...il.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] Guard pci_create_sysfs_dev_files with atomic value

On 16.03.23 14:16, Alexander Stein wrote:

> But isn't the root bridge discovered by the driver (pci-imx6 in this case) for
> that? And the driver probe path eventually calls into the sysfs file creation.
> I compared the file creation to usb, as this is a discoverable bus as well.
> There is no special initialization regarding sysfs.

If you discover a bus system you always have the option of creating of virtual
hotplug event for the root hub or host controller.
But for PCI that is a bad design choice. USB is different.

> If, for some reason, the device enumeration for PCI bus during imx6_pcie_probe
> is delayed after pci_sysfs_init initcall, this initcall essentially does
> nothing, no devices or busses to iterate. Which means the complete pcie sysfs

On your specific system. You cannot use that as a model for all systems.

> creation is done from bridge probe path. There is no reason to iterate over
> discovered PCIe devices/busses separately.

If there is no other PCI device, the loop is a nop. But otherwise it is necessary.

>>> So technically the device is not probed from within a initcall but a
>>> kthread. It is set to be probed asynchronous in imx6_pcie_driver.
>>
>> That may be the problem, respectively that system is incomplete
>> You are registering a PCI bridge. The PCI subsystem should be
>> done setting up when you run. That is just a simple dependency.
> 
> Is there such an dependency in the first place? I can't see anything, even the
> late_initcall to pci_resource_alignment_sysfs_init is a different matter.

On your hardware, yes. In the kernel, no.
That is the very point. The kernel is missing a way to represent a dependency.

	Regards
		Oliver