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

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Message-ID: <440e7c29-bee1-29f3-afa8-7b5905fd6cf2@linux.intel.com>
Date: Mon, 1 Dec 2025 11:45:28 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
cc: Bjorn Helgaas <bhelgaas@...gle.com>, 
    Matthew W Carlis <mattc@...estorage.com>, 
    ALOK TIWARI <alok.a.tiwari@...cle.com>, ashishk@...estorage.com, 
    bamstadt@...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, Maciej W. Rozycki wrote:

> Discard Vendor:Device ID matching in the PCIe failed link retraining 
> quirk and ignore the link status for the removal of the 2.5GT/s speed 
> clamp, whether applied by the quirk itself or the firmware earlier on.  
> Revert to the original target link speed if this final link retraining 
> has failed.
> 
> This is so that link training noise in hot-plug scenarios does not make 
> a link remain clamped to the 2.5GT/s speed where an event race has led 
> the quirk to apply the speed clamp for one device, only to leave it in 
> place for a subsequent device to be plugged in.
> 
> Fixes: a89c82249c37 ("PCI: Work around PCIe link training failures")
> Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
> Cc: <stable@...r.kernel.org> # v6.5+
> ---
>  drivers/pci/quirks.c |   50 ++++++++++++++++++--------------------------------
>  1 file changed, 18 insertions(+), 32 deletions(-)
> 
> linux-pcie-failed-link-retrain-unclamp-always.diff
> Index: linux-macro/drivers/pci/quirks.c
> ===================================================================
> --- linux-macro.orig/drivers/pci/quirks.c
> +++ linux-macro/drivers/pci/quirks.c
> @@ -79,11 +79,10 @@ static bool pcie_lbms_seen(struct pci_de
>   * Restrict the speed to 2.5GT/s then with the Target Link Speed field,
>   * request a retrain and check the result.
>   *
> - * If this turns out successful and we know by the Vendor:Device ID it is
> - * safe to do so, then lift the restriction, letting the devices negotiate
> - * a higher speed.  Also check for a similar 2.5GT/s speed restriction the
> - * firmware may have already arranged and lift it with ports that already
> - * report their data link being up.
> + * If this turns out successful, or where a 2.5GT/s speed restriction has
> + * been previously arranged by the firmware and the port reports its link
> + * already being up, lift the restriction, in a hope it is safe to do so,
> + * letting the devices negotiate a higher speed.
>   *
>   * Otherwise revert the speed to the original setting and request a retrain
>   * again to remove any residual state, ignoring the result as it's supposed
> @@ -94,52 +93,39 @@ static bool pcie_lbms_seen(struct pci_de
>   */
>  int pcie_failed_link_retrain(struct pci_dev *dev)
>  {
> -	static const struct pci_device_id ids[] = {
> -		{ PCI_VDEVICE(ASMEDIA, 0x2824) }, /* ASMedia ASM2824 */
> -		{}
> -	};
> -	u16 lnksta, lnkctl2;
> +	u16 lnksta, lnkctl2, oldlnkctl2;
>  	int ret = -ENOTTY;
> +	u32 lnkcap;
>  
>  	if (!pci_is_pcie(dev) || !pcie_downstream_port(dev) ||
>  	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting)
>  		return ret;
>  
>  	pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> +	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &oldlnkctl2);
>  	if (!(lnksta & PCI_EXP_LNKSTA_DLLLA) && pcie_lbms_seen(dev, lnksta)) {
> -		u16 oldlnkctl2;
> -
>  		pci_info(dev, "broken device, retraining non-functional downstream link at 2.5GT/s\n");
>  
> -		pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &oldlnkctl2);
>  		ret = pcie_set_target_speed(dev, PCIE_SPEED_2_5GT, false);
> -		if (ret) {
> -			pci_info(dev, "retraining failed\n");
> -			pcie_set_target_speed(dev, PCIE_LNKCTL2_TLS2SPEED(oldlnkctl2),
> -					      true);
> -			return ret;
> -		}
> -
> -		pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> +		if (ret)
> +			goto err;
>  	}
>  
>  	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
> -
> -	if ((lnksta & PCI_EXP_LNKSTA_DLLLA) &&
> -	    (lnkctl2 & PCI_EXP_LNKCTL2_TLS) == PCI_EXP_LNKCTL2_TLS_2_5GT &&
> -	    pci_match_id(ids, dev)) {
> -		u32 lnkcap;
> -
> +	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.

>  		pci_info(dev, "removing 2.5GT/s downstream link speed restriction\n");
> -		pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &lnkcap);
>  		ret = pcie_set_target_speed(dev, PCIE_LNKCAP_SLS2SPEED(lnkcap), false);
> -		if (ret) {
> -			pci_info(dev, "retraining failed\n");
> -			return ret;
> -		}
> +		if (ret)
> +			goto err;
>  	}
>  
>  	return ret;

return 0;

> +err:
> +	pci_info(dev, "retraining failed\n");
> +	pcie_set_target_speed(dev, PCIE_LNKCTL2_TLS2SPEED(oldlnkctl2), true);
> +	return ret;
>  }
>  
>  static ktime_t fixup_debug_start(struct pci_dev *dev,
> 

-- 
 i.