On Tue, Mar 31, 2015 at 08:09:53AM -0600, Alex Williamson wrote:
> On Tue, 2015-03-31 at 14:23 +0200, Lucas Stach wrote:
> > Am Montag, den 30.03.2015, 10:52 -0600 schrieb Alex Williamson:
> > > On Mon, 2015-03-30 at 18:06 +0200, Lucas Stach wrote:
> > > > Am Montag, den 30.03.2015, 08:33 -0600 schrieb Alex Williamson:
> > > > > On Mon, 2015-03-30 at 12:55 +0200, Lucas Stach wrote:
> > > > > > This adds a simple way to get the root port a given device
> > > > > > is connected to.
> > > > > >
> > > > > > Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> > > > > > ---
> > > > > > v2: new patch in v2
> > > > > > v3: rename to pci_find_rootport to fit better with other API
> > > > > > v4: - rename to make it obvious that this function is PCIe specific
> > > > > > - fixes wrong assumption about what is a root bus in the presence
> > > > > > virtual buses
> > > > > > ---
> > > > > > drivers/pci/search.c | 20 ++++++++++++++++++++
> > > > > > include/linux/pci.h | 1 +
> > > > > > 2 files changed, 21 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> > > > > > index a20ce7d5e2a7..d7c599103ae1 100644
> > > > > > --- a/drivers/pci/search.c
> > > > > > +++ b/drivers/pci/search.c
> > > > > > @@ -384,3 +384,23 @@ int pci_dev_present(const struct pci_device_id *ids)
> > > > > > return 0;
> > > > > > }
> > > > > > EXPORT_SYMBOL(pci_dev_present);
> > > > > > +
> > > > > > +/**
> > > > > > + * pcie_find_root_port - Returns the root port the given device is connected to.
> > > > > > + * @dev: PCI device for which the root port should be found.
> > > > > > + */
> > > > > > +struct pci_dev *pcie_find_root_port(struct pci_dev *dev)
> > > > > > +{
> > > > > > + struct pci_bus *bus = dev->bus;
> > > > > > +
> > > > > > + /* if this device is located on the root bus, it is a root port */
> > > > > > + if (pci_is_root_bus(bus))
> > > > > > + return dev;
> > > > >
> > > > > It could also be a root complex endpoint or a conventional PCI
> > > > > device/bridge sitting on the host bridge bus.
> > > >
> > > > > > +
> > > > > > + /* walk up the PCI hierarchy to the first level below the root */
> > > > > > + while (bus->parent && bus->parent->parent)
> > > > > > + bus = bus->parent;
> > > > > > +
> > > > > > + return bus->self;
> > > > > > +}
> > > > > > +EXPORT_SYMBOL(pcie_find_root_port);
> > > > >
> > > > > IMHO, this makes too many assumptions about the topology that it's
> > > > > working with for a generic interface. Your usage may be fairly fixed,
> > > > > but there are too many cases where it could return something that's not
> > > > > a root port as a general interface. Thanks,
> > > > >
> > > > I'm open to suggestions on how to improve the detection. I really need
> > > > something which works reliable in the majority of cases, as the Tegra
> > > > quirk should not be executed on other platforms.
> > > >
> > > > Do you think filtering out EP devices and conventional PCI bridges on
> > > > the root bus is enough?
> > >
> > > I'm actually pretty confused by the implementation of the quirk as well,
> > > why do you even need this pcie_find_root_port() function? Your fixup is
> > > called for every single PCI device in the system, so why do you need to
> > > go to the trouble of scanning the topology for the root port? You'll be
> > > passed the root port eventually and it will match your ID table w/o any
> > > extra effort. As coded, you're calling the set capability function
> > > multiple times per root port, once for itself and once for each device
> > > below it.
> > >
> > > Personally, I'd probably do away with the table, declare a fixup for
> > > each entry for the specific vendor/device ID, and make a simple quirk
> > > callback that sets the capability bit. Just my preference though.
> > > Thanks,
> > >
> > No, you missed the point of the fixup here.
> >
> > We need to apply this fixup on every device in the system if the root
> > port is a Tegra. So the fixup needs to get called for every device,
> > filtering on a specific vendor/device ID is not possible.
> >
> > But on the other hand this fixup may be compiled into a multiplatform
> > kernel. If this kernel is strated on a device which isn't a Tegra (and
> > so has no Tegra root port) we don't want to apply the fixup at all.
>
> Yes, you're right, sorry for the misinterpretation. So the quirk works
> as expected, but I think at a minimum the helper function needs to be
> renamed to something like pci_find_root_bus_dev() since there is no
> attempt made to verify whether the returned device is actually a root
> port. If you don't support hotplug, you could also apply the quirk from
> the root port down instead of searching from every device up. Thanks,
How should we proceed here? I agree with Alex's comments.
Bjorn
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