Re: [PATCH] PCI/portdrv: Disable bwctrl service if port is fixed at 2.5 GT/s

Niklas Schnelle
2024-12-12T20:40:11Z

On Thu, 2024-12-12 at 13:32 +0100, Lukas Wunner wrote:
> On Thu, Dec 12, 2024 at 10:17:21AM +0100, Niklas Schnelle wrote:
> > On Thu, 2024-12-12 at 10:08 +0100, Lukas Wunner wrote:
> > > After re-reading the spec I'm convinced now
> > > that we're doing this wrong and that we should honor the Max Link Speed
> > > instead of blindly deeming all set bits in the Link Capabilities 2
> > > Register as supported speeds:
> > >
> > > https://lore.kernel.org/r/e3386d62a766be6d0ef7138a001dabfe563cdff8.1733991971.git.lukas@wunner.de/
> > >
> > > @Niklas, could you test if this is sufficient to avoid the issue?
> > > Or do we still need to stop instantiating the bandwidth controller
> > > if more than one speed is supported?
> >
> > Yes, I will test this but will only get to do so tonight (UTC +2).
>
> Hey, no worries. We're not on the run!
>
> > If it's not sufficient I think we could use the modified
> > pcie_get_supported_speeds() to check if only one link speed is
> > supported, right?
>
> pcie_get_supported_speeds() is used to fill in the supported_speeds
> field in struct pci_dev.
>
> And that field is used in a number of places (exposure of the max link
> speed in sysfs, delay handling in pci_bridge_wait_for_secondary_bus(),
> link tuning in radeon/amdgpu drivers, etc).

Side question. If this is used in radeon/amdgpu could detecting the
thunderbolt port's max link speed as 2.5 GT/s cause issues for external
GPUs?