linux-kernel - Re: [PATCH] PCI: Always lift 2.5GT/s restriction in PCIe failed link retraining

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Message-ID: <alpine.DEB.2.21.2512011319590.49654@angie.orcam.me.uk>
Date: Mon, 1 Dec 2025 13:55:29 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
cc: Bjorn Helgaas <bhelgaas@...gle.com>, 
    Matthew W Carlis <mattc@...estorage.com>, 
    ALOK TIWARI <alok.a.tiwari@...cle.com>, ashishk@...estorage.com, 
    msaggi@...estorage.com, sconnor@...estorage.com, 
    Lukas Wunner <lukas@...ner.de>, Jiwei <jiwei.sun.bj@...com>, 
    guojinhui.liam@...edance.com, ahuang12@...ovo.com, sunjw10@...ovo.com, 
    linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: Always lift 2.5GT/s restriction in PCIe failed link
 retraining

On Mon, 1 Dec 2025, Ilpo Järvinen wrote:

> > +	pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &lnkcap);
> > +	if ((lnkctl2 & PCI_EXP_LNKCTL2_TLS) == PCI_EXP_LNKCTL2_TLS_2_5GT &&
> > +	    (lnkcap & PCI_EXP_LNKCAP_SLS) != PCI_EXP_LNKCAP_SLS_2_5GB) {
> 
> I'm trying to recall, if there was some particular reason why 
> ->supported_speeds couldn't be used in this function. It would avoid the 
> need to read LinkCap at all.

 Thanks for the hint.  There's probably none and it's just me missing some 
of the zillion bits and pieces.  I'll wait a couple of days for any other 
people to chime in and respin with this update included if everyone is 
otherwise happy to proceed with this update.

> > +		if (ret)
> > +			goto err;
> >  	}
> >  
> >  	return ret;
> 
> return 0;

 It can still return -ENOTTY if neither of the two latter conditionals 
matched, meaning the quirk was not applicable after all.  ISTR you had 
issues with the structure of this code before; I am not sure if it can 
be made any better in a reasonable way.  It is not a failure per se, so 
the newly-added common error path does not apply.  This is the case for: 
"Return an error if retraining was not needed[...]" from the introductory 
comment.

 Shall I add a comment above the return statement referring to this?

  Maciej