Re: [PATCH for-linus] PCI: Honor Max Link Speed when determining supported speeds

[Niklas Schnelle <niks@kernel.org>]

On Thu, 2024-12-12 at 17:58 +0100, Niklas Schnelle wrote:
> On Thu, 2024-12-12 at 10:11 -0600, Bjorn Helgaas wrote:
> > On Thu, Dec 12, 2024 at 09:56:16AM +0100, Lukas Wunner wrote:
> > > The Supported Link Speeds Vector in the Link Capabilities 2 Register
> > > indicates the *supported* link speeds.  The Max Link Speed field in
> > > the Link Capabilities Register indicates the *maximum* of those speeds.
> > > 
> > > Niklas reports that the Intel JHL7540 "Titan Ridge 2018" Thunderbolt
> > > controller supports 2.5-8 GT/s speeds, but indicates 2.5 GT/s as maximum.
> > > Ilpo recalls seeing this inconsistency on more devices.
> > > 
> > > pcie_get_supported_speeds() neglects to honor the Max Link Speed field
> > > and will thus incorrectly deem higher speeds as supported.  Fix it.
> > > 
> > > Fixes: d2bd39c0456b ("PCI: Store all PCIe Supported Link Speeds")
> > > Reported-by: Niklas Schnelle <niks@kernel.org>
> > > Closes: https://lore.kernel.org/r/70829798889c6d779ca0f6cd3260a765780d1369.camel@kernel.org/
> > > Signed-off-by: Lukas Wunner <lukas@wunner.de>
> > > Cc: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> > 
> > Looks like you want this in v6.13?  Can we make commit log more
> > explicit as to why we need it there?  Is this change enough to resolve
> > the boot hang Niklas reported?
> 
> As for if it fixes my hang I will test this later today when I come
> home. But even if it is not enough on its own, I believe that this will
> be needed as a prerequisite for the fix of my hang issue in that
> without this patch the dev->supported_speeds incorrectly shows multiple
> speeds as supported making it impossible to suppress probing of bwctrl
> for devices that only support a fixed speed.

Ok, gave this a test and as somewhat suspected this patch alone doesn't
fix my boot hang nor do I get more output (also tried Lukas suggestion
with early_printk).

Then I put my patch using the hweight8(dev->supported_speeds) > 1
condition suggested by Lukas on top and with both things work again. I
would now propose that once we've cleared up Ilpo's comment I sent a
series with both patches for you to easily pick together. If you prefer
I can of course also sent my patch stand alone.

Thanks,
Niklas