Thanks Bjorn and no issues at all about the delay -- I definitely understand how
busy we all are.
I'll go ahead and submit a PCI Quirk. As part of this, would you like me to
also commit a new PCI-E routine to find the Root Complex Port for a given
PCI Device? It seem like it might prove useful in the future. Otherwise I'll
just incorporate that loop in my PCI Quirk.
Casey
________________________________________
From: Bjorn Helgaas [bhelgaas@xxxxxxxxxx]
Sent: Friday, May 29, 2015 9:20 AM
To: Casey Leedom
Cc: netdev@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx
Subject: Re: Request for advice on where to put Root Complex "fix up" code for downstream device
Hi Casey,
Sorry, this one slipped through and I forgot to respond earlier.
On Thu, May 07, 2015 at 11:31:58PM +0000, Casey Leedom wrote:
> | From: Bjorn Helgaas [bhelgaas@xxxxxxxxxx]
> | Sent: Thursday, May 07, 2015 4:04 PM
> |
> | There are a lot of fixups in drivers/pci/quirks.c. For things that have to
> | be worked around either before a driver claims the device or if there is no
> | driver at all, the fixup *has* to go in drivers/pci/quirks.c
> |
> | But for things like this, where the problem can only occur after a driver
> | claims the device, I think it makes more sense to put the fixup in the
> | driver itself. The only wrinkle here is that the fixup has to be done on a
> | separate device, not the device claimed by the driver. But I think it
> | probably still makes sense to put this fixup in the driver.
>
> Okay, the example code that I provided (still quoted below) was indeed
> done as a fix within the cxgb4 Network Driver. I've also worked up a
> version as a PCI Quirk but if you and David Miller agree that the fixup
> code should go into cxgb4, I'm comfortable with that. I can also provide
> the example PCI Quirk code I worked up if you like.
>
> One complication to doing this in cxgb4 is that it attaches to Physical
> Function 4 of our T5 chip. Meanwhile, a completely separate storage
> driver, csiostor, connections to PF5 and PF6 and there's no
> requirement at all that cxgb4 be loaded. So if we go down the road of
> putting the fixup code in the cxgb4 driver, we'll also need to duplicate
> that code in the csiostor driver.
Sounds simpler to just put the quirk in drivers/pci/quirks.c.
> | > +static void clear_root_complex_tlp_attributes(struct pci_dev *pdev)
> | > +{
> | > + struct pci_bus *bus = pdev->bus;
> | > + struct pci_dev *highest_pcie_bridge = NULL;
> | > +
> | > + while (bus) {
> | > + struct pci_dev *bridge = bus->self;
> | > +
> | > + if (!bridge || !bridge->pcie_cap)
> | > + break;
> | > + highest_pcie_bridge = bridge;
> | > + bus = bus->parent;
> | > + }
> |
> | Can you use pci_upstream_bridge() here? There are a couple places where we
> | want to find the Root Port, so we might factor that out someday. It'll be
> | easier to find all those places if they use with pci_upstream_bridge().
>
> It looks like pci_upstream_bridge() just traverses one like upstream toward the
> Root Complex? Or am I misunderstanding that function?
No, you're right. I was just trying to suggest using pci_upstream_bridge()
instead of bus->parent->self in your loop. It wouldn't replace the loop
completely.
Bjorn
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