linux-kernel - Re: [PATCH] PCI/ASPM: Wait for data link active after retraining

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Date:   Mon, 26 Sep 2022 10:59:47 +1000
From:   Nathan Rossi <nathan@...hanrossi.com>
To:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Nathan Rossi <nathan.rossi@...i.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI/ASPM: Wait for data link active after retraining

On Thu, 2 Jun 2022 at 16:55, Nathan Rossi <nathan@...hanrossi.com> wrote:
>
> From: Nathan Rossi <nathan.rossi@...i.com>
>
> When retraining the link either the child or the parent device may have
> the data link layer state machine of the respective devices move out of
> the active state despite the physical link training being completed.
> Depending on how long is takes for the devices to return to the active
> state, the device may not be ready and any further reads/writes to the
> device can fail.
>
> This issue is present with the pci-mvebu controller paired with a device
> supporting ASPM but without advertising the Slot Clock, where during
> boot the pcie_aspm_cap_init call would cause common clocks to be made
> consistent and then retrain the link. However the data link layer would
> not be active before any device initialization (e.g. ASPM capability
> queries, BAR configuration) causing improper configuration of the device
> without error.
>
> To ensure the child device is accessible, after the link retraining use
> pcie_wait_for_link to perform the associated state checks and any needed
> delays.
>
> Signed-off-by: Nathan Rossi <nathan.rossi@...i.com>
> ---

Just pinging this patch, are there any comments or feedback for this change?

Thanks,
Nathan

>  drivers/pci/pcie/aspm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index a96b7424c9..4b8a1810be 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -288,7 +288,8 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
>                 reg16 &= ~PCI_EXP_LNKCTL_CCC;
>         pcie_capability_write_word(parent, PCI_EXP_LNKCTL, reg16);
>
> -       if (pcie_retrain_link(link))
> +       /* Retrain link and then wait for the link to become active */
> +       if (pcie_retrain_link(link) && pcie_wait_for_link(parent, true))
>                 return;
>
>         /* Training failed. Restore common clock configurations */
> ---
> 2.36.1