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

[Mika Westerberg]

On Sat, Dec 07, 2024 at 07:44:09PM +0100, Niklas Schnelle wrote:
> Trying to enable bwctrl on a Thunderbolt port causes a boot hang on some
> systems though the exact reason is not yet understood. As per the spec
> Thunderbolt PCIe Downstream Ports have a fake Max Link Speed of 2.5 GT/s
> (USB4 v2 sec 11.2.1):
> 
>    "Max Link Speed field in the Link Capabilities Register set to 0001b
>     (data rate of 2.5 GT/s only).
>     Note: These settings do not represent actual throughput.
>     Throughput is implementation specific and based on the USB4 Fabric
>     performance."
> 
> More generally if 2.5 GT/s is the only supported link speed there is no
> point in throtteling as this is already the lowest possible PCIe speed
> so don't advertise the capability stopping bwctrl from being probed on
> these ports.
> 
> Link: https://lore.kernel.org/linux-pci/Z1R4VNwCOlh9Sg9n@xxxxxxxxx/
> Fixes: 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller")
> Tested-by: Niklas Schnelle <niks@xxxxxxxxxx>
> Signed-off-by: Niklas Schnelle <niks@xxxxxxxxxx>

Makes sense to me,

Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>