linux-kernel - Re: [RFC] PCI: Fix the issue of link speed downgrade after link retraining

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Message-ID: <Zy3x_QK0vZHOFZvF@wunner.de>
Date: Fri, 8 Nov 2024 12:11:57 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Bjorn Helgaas <helgaas@...nel.org>,
	"Maciej W. Rozycki" <macro@...am.me.uk>
Cc: Jinhui Guo <guojinhui.liam@...edance.com>, bhelgaas@...gle.com,
	macro@...am.me.uk, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ilpo Jarvinen <ilpo.jarvinen@...ux.intel.com>
Subject: Re: [RFC] PCI: Fix the issue of link speed downgrade after link
 retraining

[+cc Maciej, Ilpo]

On Thu, Nov 07, 2024 at 09:34:38AM -0600, Bjorn Helgaas wrote:
> On Thu, Nov 07, 2024 at 10:37:58PM +0800, Jinhui Guo wrote:
> > The link speed is downgraded to 2.5 GT/s when a Samsung NVMe device
> > is hotplugged into a Intel PCIe root port [8086:0db0].
> > 
> > ```
> > +-[0000:3c]-+-00.0  Intel Corporation Ice Lake Memory Map/VT-d
> > |           ...
> > |           +02.0-[3d]----00.0  Samsung Electronics Co Ltd Device a80e
> > ```
> > 
> > Some printing information can be obtained when the issue emerges.
> > "Card present" is reported twice via external interrupts due to
> > a slight tremor when the Samsung NVMe device is plugged in.
> > The failure of the link activation for the first time leads to
> > the link speed of the root port being mistakenly downgraded to 2.5G/s.
> > 
> > ```
> > [ 8223.419682] pcieport 0000:3d:02.0: pciehp: Slot(1): Card present
> > [ 8224.449714] pcieport 0000:3d:02.0: broken device, retraining non-functional downstream link at 2.5GT/s
> > [ 8225.518723] pcieport 0000:3d:02.0: pciehp: Slot(1): Card present
> > [ 8225.518726] pcieport 0000:3d:02.0: pciehp: Slot(1): Link up
> > ```
> > 
> > To avoid wrongly setting the link speed to 2.5GT/s, only allow
> > specific pcie devices to perform link retrain.

With which kernel version are you seeing this?

A set of fixes for the 2.5GT/s retraining feature appeared in v6.12-rc1,
specifically f68dea13405c ("PCI: Revert to the original speed after PCIe
failed link retraining").

Have you tested whether the latest v6.12 rc is still affected?

Thanks,

Lukas

> > Fixes: a89c82249c37 ("PCI: Work around PCIe link training failures")
> > Signed-off-by: Jinhui Guo <guojinhui.liam@...edance.com>
> > ---
> >  drivers/pci/quirks.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index dccb60c1d9cc..59858156003b 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -91,7 +91,8 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
> >  	int ret = -ENOTTY;
> >  
> >  	if (!pci_is_pcie(dev) || !pcie_downstream_port(dev) ||
> > -	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting)
> > +	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting ||
> > +		!pci_match_id(ids, dev))
> >  		return ret;
> >  
> >  	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
> > @@ -119,8 +120,7 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
> >  	}
> >  
> >  	if ((lnksta & PCI_EXP_LNKSTA_DLLLA) &&
> > -	    (lnkctl2 & PCI_EXP_LNKCTL2_TLS) == PCI_EXP_LNKCTL2_TLS_2_5GT &&
> > -	    pci_match_id(ids, dev)) {
> > +	    (lnkctl2 & PCI_EXP_LNKCTL2_TLS) == PCI_EXP_LNKCTL2_TLS_2_5GT) {
> >  		u32 lnkcap;
> >  
> >  		pci_info(dev, "removing 2.5GT/s downstream link speed restriction\n");
> > -- 
> > 2.20.1