linux-kernel - Ping: [PATCH] PCI/ASPM: Don't retrain link if ASPM not possible.

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Date:   Wed, 30 Nov 2016 09:11:11 -0800
From:   David Daney <ddaney@...iumnetworks.com>
To:     <linux-pci@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>
CC:     <linux-kernel@...r.kernel.org>, Andy Lutomirski <luto@...nel.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        David Daney <david.daney@...ium.com>
Subject: Ping: [PATCH] PCI/ASPM: Don't retrain link if ASPM not possible.

On 11/17/2016 02:25 PM, David Daney wrote:
> From: David Daney <david.daney@...ium.com>
>
> Some (defective) PCIe devices are not able to reliably do link
> retraining.
>
> Check to see if ASPM is possible between link partners before
> configuring common clocking, and doing the resulting link retraining.
> If ASPM is not possible, there is no reason to risk losing access to a
> device due to an unnecessary link retraining.
>

Hi Bjorn,

It has been a couple of weeks since I originally sent this, and I wanted 
to know if you have had a chance to look at it.  If possible, it would 
be nice to consider for the approaching merge window.

Thanks,
David Daney


> Signed-off-by: David Daney <david.daney@...ium.com>
> ---
>   drivers/pci/pcie/aspm.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 0ec649d..d6667db 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -351,12 +351,26 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>   		return;
>   	}
>
> +	/* Get upstream/downstream components' register state */
> +	pcie_get_aspm_reg(parent, &upreg);
> +	child = list_entry(linkbus->devices.next, struct pci_dev, bus_list);
> +	pcie_get_aspm_reg(child, &dwreg);
> +
> +	/*
> +	 * If ASPM not supported, don't mess with the clocks and link,
> +	 * bail out now.
> +	 */
> +	if (!(upreg.support & dwreg.support))
> +		return;
> +
>   	/* Configure common clock before checking latencies */
>   	pcie_aspm_configure_common_clock(link);
>
> -	/* Get upstream/downstream components' register state */
> +	/*
> +	 * Re-read upstream/downstream components' register state
> +	 * after clock configuration
> +	 */
>   	pcie_get_aspm_reg(parent, &upreg);
> -	child = list_entry(linkbus->devices.next, struct pci_dev, bus_list);
>   	pcie_get_aspm_reg(child, &dwreg);
>
>   	/*
>