linux-kernel - Re: [PATCH v1 1/2] PCI/ASPM: Disable ASPM L1.2 Substate if we don't have LTR

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Date:   Fri, 20 Apr 2018 14:22:06 +0530
From:   Srinath Mannam <srinath.mannam@...adcom.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Sinan Kaya <okaya@...eaurora.org>,
        Rajat Jain <rajatja@...gle.com>,
        Ray Jui <ray.jui@...adcom.com>,
        Keith Busch <keith.busch@...el.com>,
        linux-acpi@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] PCI/ASPM: Disable ASPM L1.2 Substate if we don't
 have LTR

Hi Bjorn,

I have verified this patch, it works fine for me.

Thanks & Regards,
Srinath.

On Fri, Apr 20, 2018 at 2:35 AM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
>
> When in the ASPM L1.0 state (but not the PCI-PM L1.0 state), the most
> recent LTR value and the LTR_L1.2_THRESHOLD determines whether the link
> enters the L1.2 substate.
>
> If we don't have LTR enabled, prevent the use of ASPM L1.2.
>
> PCI-PM L1.2 may still be used because it doesn't depend on
> LTR_L1.2_THRESHOLD (see PCIe r4.0, sec 5.5.1).
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/pcie/aspm.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index f76eb7704f64..c687c817b47d 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -400,6 +400,15 @@ static void pcie_get_aspm_reg(struct pci_dev *pdev,
>                 info->l1ss_cap = 0;
>                 return;
>         }
> +
> +       /*
> +        * If we don't have LTR for the entire path from the Root Complex
> +        * to this device, we can't use ASPM L1.2 because it relies on the
> +        * LTR_L1.2_THRESHOLD.  See PCIe r4.0, secs 5.5.4, 6.18.
> +        */
> +       if (!pdev->ltr_path)
> +               info->l1ss_cap &= ~PCI_L1SS_CAP_ASPM_L1_2;
> +
>         pci_read_config_dword(pdev, info->l1ss_cap_ptr + PCI_L1SS_CTL1,
>                               &info->l1ss_ctl1);
>         pci_read_config_dword(pdev, info->l1ss_cap_ptr + PCI_L1SS_CTL2,
>