Re: trouble with PCI: Call pci_read_bridge_bases() from core instead of arch code

[Bjorn Helgaas <bhelgaas@google.com>]

Hi Lorenzo, thanks for jumping on this!

On Wed, Sep 02, 2015 at 06:47:16PM +0100, Lorenzo Pieralisi wrote:
> Hi Hannes,
> 
> On Wed, Sep 02, 2015 at 10:51:18AM +0100, oe5hpm wrote:
> > Hi Lorenzo,
> > 
> > today i tried to boot up the most recent vanilla kernel on my
> > Freescale i.mx6 board.
> > I ran into trouble regarding PCI enumeration.
> > 
> > [    0.431949] imx6q-pcie 1ffc000.pcie: PCI host bridge to bus 0000:00
> > [    0.431976] pci_bus 0000:00: root bus resource [io  0x1000-0xffff]
> > [    0.431996] pci_bus 0000:00: root bus resource [mem 0x01000000-0x01efffff]
> > [    0.432022] pci_bus 0000:00: root bus resource [bus 00-ff]
> > [    0.433271] PCI: bus0: Fast back to back transfers disabled
> > [    0.433629] pci 0000:00:00.0: PCI bridge to [bus 01-ff]
> > [    0.435181] PCI: bus1: Fast back to back transfers disabled
> > [    0.435564] pci 0000:00:00.0: BAR 0: assigned [mem 0x01000000-0x010fffff]
> > [    0.435593] pci 0000:00:00.0: BAR 8: no space for [mem size 0x01000000]
> > [    0.435613] pci 0000:00:00.0: BAR 8: failed to assign [mem size 0x01000000]
> > [    0.435635] pci 0000:00:00.0: BAR 9: assigned [mem
> > 0x01100000-0x011fffff pref]
> > [    0.435655] pci 0000:00:00.0: BAR 6: assigned [mem
> > 0x01200000-0x0120ffff pref]
> > [    0.435676] pci 0000:00:00.0: BAR 7: assigned [io  0x1000-0x1fff]
> > [    0.435705] pci 0000:01:00.0: BAR 2: no space for [mem size 0x00200000]
> > [    0.435722] pci 0000:01:00.0: BAR 2: failed to assign [mem size 0x00200000]
> > [    0.435739] pci 0000:01:00.0: BAR 1: no space for [mem size 0x00004000]
> > [    0.435754] pci 0000:01:00.0: BAR 1: failed to assign [mem size 0x00004000]
> > [    0.435770] pci 0000:01:00.0: BAR 0: no space for [mem size 0x00000100]
> > [    0.435786] pci 0000:01:00.0: BAR 0: failed to assign [mem size 0x00000100]
> > [    0.435804] pci 0000:00:00.0: PCI bridge to [bus 01]
> > [    0.435826] pci 0000:00:00.0:   bridge window [io  0x1000-0x1fff]
> > [    0.435855] pci 0000:00:00.0:   bridge window [mem
> > 0x01100000-0x011fffff pref]
> > 
> > there are several fails assigning memory ressources to pci-devices.
> > 
> > i bisect down this trouble to commit id:
> > dff22d2054b5dbb1889f20c03959dd0c494fab8c : PCI: Call
> > pci_read_bridge_bases() from core instead of arch code
> > 
> > For testing purpose i've reverted this commit on a local branch and
> > everythings works fine, as before.
> > 
> > [    0.431976] imx6q-pcie 1ffc000.pcie: PCI host bridge to bus 0000:00
> > [    0.432004] pci_bus 0000:00: root bus resource [io  0x1000-0xffff]
> > [    0.432023] pci_bus 0000:00: root bus resource [mem 0x01000000-0x01efffff]
> > [    0.432047] pci_bus 0000:00: root bus resource [bus 00-ff]
> > [    0.433302] PCI: bus0: Fast back to back transfers disabled
> > [    0.435122] PCI: bus1: Fast back to back transfers disabled
> > [    0.435504] pci 0000:00:00.0: BAR 0: assigned [mem 0x01000000-0x010fffff]
> > [    0.435535] pci 0000:00:00.0: BAR 8: assigned [mem 0x01100000-0x013fffff]
> > [    0.435557] pci 0000:00:00.0: BAR 6: assigned [mem
> > 0x01400000-0x0140ffff pref]
> > [    0.435585] pci 0000:01:00.0: BAR 2: assigned [mem 0x01200000-0x013fffff]
> > [    0.435626] pci 0000:01:00.0: BAR 1: assigned [mem 0x01100000-0x01103fff]
> > [    0.435665] pci 0000:01:00.0: BAR 0: assigned [mem 0x01104000-0x011040ff]
> > [    0.435703] pci 0000:00:00.0: PCI bridge to [bus 01]
> > [    0.435728] pci 0000:00:00.0:   bridge window [mem 0x01100000-0x013fffff]
> > 
> > Further i can break down the failure to "drivers/pci/probe.c" line #924.
> > If i comment out the "pci_read_bridge_bases(child);" also everything works well.
> > 
> > I have to confess, that my knowledge about the whole PCI thing in the
> > kernel is not very deep, so it is not possible for me to figure out
> > what is going wrong.
> 
> It looks like a bogus bridge aperture size is causing this to happen,
> and this prevents reassignment on arm (bridge aperture is too big),
> which proves that reading the bridge bases without vetting the corresponding
> resources may break (on platforms that were not reading them before).
> 
> arm was the only platform not reading the bridge bases, here is an
> answer why. So, to prevent reverting the commit I put together this
> patch (to be reworked if we deem it reasonable), subject to discussion
> (I fear it may end up breaking other arm platforms, I do not have all
> ARM boards and required host controllers to test, I managed to test it on
> an iMX6 Sabrelite though).
> 
> Here, please let me know if it works for you, I will keep on thinking
> to find the best solution.
> 
> I will have to do this for arm64 too, comments very welcome.
> 
> Thanks,
> Lorenzo
> 
> -- >8 --
> Subject: [PATCH] arm: kernel: pci: fixup erroneous PCI bridge apertures
> 
> Bridge apertures read by core PCI code through pci_read_bridge_bases()
> might be erroneous (bogus platform setup). If the arch code does not vet
> the bridge resources (ie by trying to claim them), we can end up in a
> situation where wrong bridge apertures can prevent resources assignment
> for downstream devices causing enumeration failures (eg a bridge
> aperture does not fit in the respective host controller resource window,
> so it can't be assigned).
> 
> This patch adds arm arch code that vets bridge resources by trying
> to claim them, and reset them on claiming failure so that they can
> be properly reassigned.

We definitely should not depend on the platform to set up the bridge
windows.  Do we know what the platform left in the 00:00.0 window
registers?

I see that bus 01 requires 0x204100 of mem space, which must be
rounded up to a megabyte boundary, so the window must be at least 3M
(0x00300000):

  pci 0000:01:00.0: BAR 2: failed to assign [mem size 0x00200000]
  pci 0000:01:00.0: BAR 1: failed to assign [mem size 0x00004000]
  pci 0000:01:00.0: BAR 0: failed to assign [mem size 0x00000100]

I don't understand the connection with dff22d2054b5 yet.  If we don't
call pci_read_bridge_bases(), apparently some assign-resources path
figures out the required size and assigns a 3M window.

If we *do* call pci_read_bridge_bases(), do we read a bogus 16M window
size, fail to assign that because the host controller window isn't big
enough, and then the assign-resources path just gives up?  I assume
clearing r->flags in your patch is the critical thing?  Is there
something in assign-resources that checks for r->flags == 0?

I think it would be ideal if we could someday claim the resource
immediately, as soon as we read it from a BAR or bridge window, and
mark it as IORESOURCE_UNSET if claiming it fails.  Then if the
platform set up reasonable windows, we could use them; if it didn't,
we could just assign our own.

I'd like to avoid adding things to pcibios_fixup_bus() if possible
because most of what is done there is arch-independent, and I'd like
to get the arch-independent stuff into the PCI core.

Bjorn

> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> ---
>  arch/arm/kernel/bios32.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
> index 874e182..ebbe052 100644
> --- a/arch/arm/kernel/bios32.c
> +++ b/arch/arm/kernel/bios32.c
> @@ -282,6 +282,27 @@ static inline int pdev_bad_for_parity(struct pci_dev *dev)
>  
>  }
>  
> +static void pcibios_fixup_bridge_resources(struct pci_dev *dev)
> +{
> +	int idx;
> +
> +	if (!dev->bus)
> +		return;
> +
> +	for (idx = PCI_BRIDGE_RESOURCES; idx < PCI_NUM_RESOURCES; idx++) {
> +		struct resource *r = &dev->resource[idx];
> +
> +		if (!r->flags || r->parent)
> +			continue;
> +
> +		if (pci_claim_resource(dev, idx)) {
> +			r->flags = 0;
> +			r->start = 0;
> +			r->end = -1;
> +		}
> +	}
> +}
> +
>  /*
>   * pcibios_fixup_bus - Called after each bus is probed,
>   * but before its children are examined.
> @@ -352,6 +373,9 @@ void pcibios_fixup_bus(struct pci_bus *bus)
>  			bus->bridge_ctl |= PCI_BRIDGE_CTL_PARITY;
>  	}
>  
> +	if (bus->self)
> +		pcibios_fixup_bridge_resources(bus->self);
> +
>  	/*
>  	 * Report what we did for this bus
>  	 */
> -- 
> 1.9.1
> 
>