PCI: Allow built-in drivers to use async initial probing

JIRA: https://issues.redhat.com/browse/RHEL-107898
Upstream Status: 9170304

commit 9170304
Author: Lukas Wunner <lukas@wunner.de>
Date:   Fri Jul 4 09:38:33 2025 +0200

    PCI: Allow built-in drivers to use async initial probing

    The PCI core has historically not allowed built-in drivers to opt in to
    async initial probing:  Drivers may set "PROBE_PREFER_ASYNCHRONOUS", but
    initial probing always happens synchronously.  That's because the PCI core
    uses device_attach() instead of device_initial_probe().

    Should a driver return -EPROBE_DEFER on initial probe, reprobing later on
    does honor the PROBE_PREFER_ASYNCHRONOUS setting.  Modular drivers are
    also allowed to probe asynchronously, which is inconsistent.

    The choice of device_attach() is likely not deliberate:  It was introduced
    in 2013 with commit 58d9a38 ("PCI: Skip attaching driver in
    device_add()"), but asynchronous probing was added two years later with
    commit 765230b ("driver-core: add asynchronous probing support for
    drivers").

    According to the kernel-doc of "enum probe_type", "the end goal is to
    switch the kernel to use asynchronous probing by default".  To this end,
    use device_initial_probe() to allow asynchronous initial probing.  The
    function returns void, making the return value check unnecessary.

    Initial PCI probing often takes on the order of seconds even on laptops,
    so this may speed up booting significantly.

    A small number of PCI drivers already opt in to asynchronous probing.
    Their maintainers (who are all cc'ed) should watch out for issues, now
    that asynchronous probing is not just allowed for deferred and modular
    probing, but also initial probing:

      hl_pci_driver        drivers/accel/habanalabs/common/habanalabs_drv.c
      cxl_pci_driver       drivers/cxl/pci.c
      quicki2c_driver      drivers/hid/intel-thc-hid/intel-quicki2c/pci-quicki2c.c
      quickspi_driver      drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c
      i801_driver          drivers/i2c/busses/i2c-i801.c
      mei_me_driver        drivers/misc/mei/pci-me.c
      mei_vsc_drv          drivers/misc/mei/platform-vsc.c
      sdhci_driver         drivers/mmc/host/sdhci-pci-core.c
      nvme_driver          drivers/nvme/host/pci.c
      ehci_pci_driver      drivers/usb/host/ehci-pci.c
      hvfb_pci_stub_driver drivers/video/fbdev/hyperv_fb.c

    All other driver maintainers may test asynchronous probing by specifying
    the command line parameter "driver_async_probe=drv_name1,drv_name2,...",
    and on success setting "probe_type = PROBE_PREFER_ASYNCHRONOUS" in the
    pci_driver struct.

    Signed-off-by: Lukas Wunner <lukas@wunner.de>
    [bhelgaas: updated commit log per https://lore.kernel.org/r/aHYUh7WoDlhHckxd@wunner.de]
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Link: https://patch.msgid.link/53abe6f5ac7c631f95f5d061aa748b192eda0379.1751614426.git.lukas@wunner.de

Signed-off-by: Myron Stowe <mstowe@redhat.com>

Author: Myron Stowe

drivers/pci/bus.c

@@ -382,7 +382,6 @@ void pci_bus_add_device(struct pci_dev *dev)
 {
 	struct device_node *dn = dev->dev.of_node;
 	struct platform_device *pdev;
-	int retval;
 
 	/*
 	 * Can not put in pci_device_add yet because resources
@@ -415,9 +414,7 @@ void pci_bus_add_device(struct pci_dev *dev)
 	if (!dn || of_device_is_available(dn))
 		pci_dev_allow_binding(dev);
 
-	retval = device_attach(&dev->dev);
-	if (retval < 0 && retval != -EPROBE_DEFER)
-		pci_warn(dev, "device attach failed (%d)\n", retval);
+	device_initial_probe(&dev->dev);
 
 	pci_dev_assign_added(dev);
 }