Re: [PATCH] PCI: Fix legacy IRQ assignment execution stage

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Sep 28, 2017 at 12:37:07PM +0100, Lorenzo Pieralisi wrote:
> Through struct pci_host_bridge->{map/swizzle}_irq() hooks is now
> possible to define IRQ mapping functions on a per PCI host bridge basis.
> 
> Actual IRQ allocation is carried out by the pci_assign_irq() function in
> pci_device_probe() - to make sure a device is assigned an IRQ only if it
> is probed (ie match a driver); it retrieves a struct pci_host_bridge*
> for a given PCI device and through {map/swizzle}_irq() hooks it carries
> out the PCI IRQ allocation.
> 
> As it turned out, some legacy drivers (eg IDE layer) require that a
> device allocates IRQ as soon as it is added so that its actual IRQ
> settings are available early in the boot process. With current code
> calling pci_assign_irq() in pci_device_probe() IDE IRQ probing fails
> for some drivers:

I think the patch is fine, but I don't understand the changelog.  I
want to know specifically what the dependency on dev->irq is.  "Early
in the boot process" is pretty vague.

I *thought* we were doing something like this:

  pci_device_probe(dev1)
    pci_assign_irq(dev1)
      ...
        ide_pci_init_two(dev1, dev2, ...)
          do_ide_setup_pci_device(dev1)
            pciirq = dev1->irq                # this one is fine
          do_ide_setup_pci_device(dev2)
            pciirq = dev2->irq                # not fine

where the problem is that we haven't called pci_assign_irq(dev2), so
dev2->irq hasn't been set.

But that doesn't match the data because we should be coming through
cmd64x_init_one(), which calls ide_pci_init_one(), so we shouldn't
have a dev2 in this path.

> ide0: disabled, no IRQ
> ide0: failed to initialize IDE interface
> ide0: disabling port
> cmd64x 0000:00:02.0: IDE controller (0x1095:0x0646 rev 0x07)
> CMD64x_IDE 0000:00:02.0: BAR 0: can't reserve [io  0x8050-0x8057]
> cmd64x 0000:00:02.0: can't reserve resources
> CMD64x_IDE: probe of 0000:00:02.0 failed with error -16
> ide_generic: please use "probe_mask=0x3f" module parameter for probing
> all legacy ISA IDE ports
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x94/0xd0
> sysfs: cannot create duplicate filename '/class/ide_port/ide0'
> ...
> 
> Trace:
> [<fffffc00003308a0>] __warn+0x160/0x190
> [<fffffc000048c9f4>] sysfs_warn_dup+0x94/0xd0
> [<fffffc0000330928>] warn_slowpath_fmt+0x58/0x70
> [<fffffc000048c9f4>] sysfs_warn_dup+0x94/0xd0
> [<fffffc0000486d40>] kernfs_path_from_node+0x30/0x60
> [<fffffc00004874ac>] kernfs_put+0x16c/0x2c0
> [<fffffc00004874ac>] kernfs_put+0x16c/0x2c0
> [<fffffc000048d010>] sysfs_do_create_link_sd.isra.2+0x100/0x120
> [<fffffc00005b9d64>] device_add+0x2a4/0x7c0
> [<fffffc00005ba5cc>] device_create_groups_vargs+0x14c/0x170
> [<fffffc00005ba518>] device_create_groups_vargs+0x98/0x170
> [<fffffc00005ba690>] device_create+0x50/0x70
> [<fffffc00005df36c>] ide_host_register+0x48c/0xa00
> [<fffffc00005df330>] ide_host_register+0x450/0xa00
> [<fffffc00005ba2a0>] device_register+0x20/0x50
> [<fffffc00005df330>] ide_host_register+0x450/0xa00
> [<fffffc00005df944>] ide_host_add+0x64/0xe0
> [<fffffc000079b41c>] kobject_uevent_env+0x16c/0x710
> [<fffffc0000310288>] do_one_initcall+0x68/0x260
> [<fffffc00007b13bc>] kernel_init+0x1c/0x1a0
> [<fffffc00007b13a0>] kernel_init+0x0/0x1a0
> [<fffffc0000311868>] ret_from_kernel_thread+0x18/0x20
> [<fffffc00007b13a0>] kernel_init+0x0/0x1a0
> 
> ---[ end trace 24a70433c3e4d374 ]---
> ide0: disabling port
> 
> Fix the IRQ allocation issue by moving the pci_assign_irq() call from
> pci_device_probe() to pci_device_add(), so that IRQs for a given PCI
> device are allocated as soon as it is scanned by the PCI enumeration.
> 
> This has the drawback of allocating an IRQ even for PCI devices that
> do not have a matching kernel driver but it should be safe to carry
> out in all configurations.
> 
> Fixes: 30fdfb929e82 ("PCI: Add a call to pci_assign_irq() in
> pci_device_probe()")
> Link: http://lkml.kernel.org/r/32ec730f-c1b0-5584-cd35-f8a809122b96@roeck-us.net
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Matt Turner <mattst88@gmail.com>
> ---
>  drivers/pci/pci-driver.c | 2 --
>  drivers/pci/probe.c      | 3 +++
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 11bd267..750d688 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -415,8 +415,6 @@ static int pci_device_probe(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	struct pci_driver *drv = to_pci_driver(dev->driver);
>  
> -	pci_assign_irq(pci_dev);
> -
>  	error = pcibios_alloc_irq(pci_dev);
>  	if (error < 0)
>  		return error;
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ff94b69..ba4e466 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2103,6 +2103,9 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
>  	/* Initialize various capabilities */
>  	pci_init_capabilities(dev);
>  
> +	/* Assign device IRQ number */

Pointless comment (as is the existing capabilities one above).

> +	pci_assign_irq(dev);
> +
>  	/*
>  	 * Add the device to our list of discovered devices
>  	 * and the bus list for fixup functions, etc.
> -- 
> 2.4.12
> 
> 
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