linux-kernel - Re: [PATCH 1/2] PCI: Correct error reporting with PCIe failed link retraining

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Message-ID: <f4eafdbc-b295-a982-fe8e-dbd11b98d56f@linux.intel.com>
Date: Mon, 12 Feb 2024 14:01:25 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
cc: Bjorn Helgaas <bhelgaas@...gle.com>, 
    Mika Westerberg <mika.westerberg@...ux.intel.com>, 
    linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] PCI: Correct error reporting with PCIe failed link
 retraining

On Sat, 10 Feb 2024, Maciej W. Rozycki wrote:

> Only return successful completion status from `pcie_failed_link_retrain' 
> if retraining has actually been done, preventing excessive delays from 
> being triggered at call sites in a hope that communication will finally 
> be established with the downstream device where in fact nothing has been 
> done about the link in question that would justify such a hope.
> 
> Fixes: a89c82249c37 ("PCI: Work around PCIe link training failures")
> Reported-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Link: https://lore.kernel.org/r/aa2d1c4e-9961-d54a-00c7-ddf8e858a9b0@linux.intel.com/
> Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
> Cc: stable@...r.kernel.org # v6.5+

Thanks.

The original thread might be useful for context if somebody has to look at 
this change later on from the history, so:

Link: https://lore.kernel.org/linux-pci/20240129112710.2852-2-ilpo.jarvinen@linux.intel.com/T/#u

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.

> ---
>  drivers/pci/quirks.c |   18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> linux-pcie-failed-link-retrain-status-fix.diff
> Index: linux-macro/drivers/pci/quirks.c
> ===================================================================
> --- linux-macro.orig/drivers/pci/quirks.c
> +++ linux-macro/drivers/pci/quirks.c
> @@ -74,7 +74,8 @@
>   * firmware may have already arranged and lift it with ports that already
>   * report their data link being up.
>   *
> - * Return TRUE if the link has been successfully retrained, otherwise FALSE.
> + * Return TRUE if the link has been successfully retrained, otherwise FALSE,
> + * also when retraining was not needed in the first place.
>   */
>  bool pcie_failed_link_retrain(struct pci_dev *dev)
>  {
> @@ -83,10 +84,11 @@ bool pcie_failed_link_retrain(struct pci
>  		{}
>  	};
>  	u16 lnksta, lnkctl2;
> +	bool ret = false;
>  
>  	if (!pci_is_pcie(dev) || !pcie_downstream_port(dev) ||
>  	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting)
> -		return false;
> +		return ret;
>  
>  	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
>  	pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> @@ -98,9 +100,10 @@ bool pcie_failed_link_retrain(struct pci
>  		lnkctl2 |= PCI_EXP_LNKCTL2_TLS_2_5GT;
>  		pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, lnkctl2);
>  
> -		if (pcie_retrain_link(dev, false)) {
> +		ret = pcie_retrain_link(dev, false) == 0;
> +		if (!ret) {
>  			pci_info(dev, "retraining failed\n");
> -			return false;
> +			return ret;
>  		}
>  
>  		pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> @@ -117,13 +120,14 @@ bool pcie_failed_link_retrain(struct pci
>  		lnkctl2 |= lnkcap & PCI_EXP_LNKCAP_SLS;
>  		pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, lnkctl2);
>  
> -		if (pcie_retrain_link(dev, false)) {
> +		ret = pcie_retrain_link(dev, false) == 0;
> +		if (!ret) {
>  			pci_info(dev, "retraining failed\n");
> -			return false;
> +			return ret;
>  		}
>  	}
>  
> -	return true;
> +	return ret;
>  }
>  
>  static ktime_t fixup_debug_start(struct pci_dev *dev,
>