linux-kernel - Re: [PATCH V1] PCI/ASPM: Skip L1SS save/restore if not already enabled

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Date:   Thu, 19 Jan 2023 22:21:57 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     bhelgaas@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        rafael.j.wysocki@...el.com, enriquezmark36@...il.com,
        tasev.stefanoska@...net.be, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, treding@...dia.com,
        jonathanh@...dia.com, kthota@...dia.com, mmaddireddy@...dia.com,
        sagar.tv@...il.com
Subject: Re: [PATCH V1] PCI/ASPM: Skip L1SS save/restore if not already enabled

Hi Vidya,

On Thu, Jan 19, 2023 at 5:49 PM Vidya Sagar <vidyas@...dia.com> wrote:
>
> Skip save and restore of ASPM L1 Sub-States specific registers if they
> are not already enabled in the system. This is to avoid issues observed
> on certain platforms during restoration process, particularly when
> restoring the L1SS registers contents.
>
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=216782
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
>  drivers/pci/pcie/aspm.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 53a1fa306e1e..5d3f09b0a6a9 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -757,15 +757,29 @@ static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
>                                 PCI_L1SS_CTL1_L1SS_MASK, val);
>  }
>
> +static bool skip_l1ss_restore;

Maybe move it inside "struct pci_dev"?

Kai-Heng

> +
>  void pci_save_aspm_l1ss_state(struct pci_dev *dev)
>  {
>         struct pci_cap_saved_state *save_state;
>         u16 l1ss = dev->l1ss;
> -       u32 *cap;
> +       u32 *cap, val;
>
>         if (!l1ss)
>                 return;
>
> +       /*
> +        * Skip save and restore of L1 Sub-States registers if they are not
> +        * already enabled in the system
> +        */
> +       pci_read_config_dword(dev, l1ss + PCI_L1SS_CTL1, &val);
> +       if (!(val & PCI_L1SS_CTL1_L1SS_MASK)) {
> +               skip_l1ss_restore = 1;
> +               return;
> +       }
> +
> +       skip_l1ss_restore = 0;
> +
>         save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
>         if (!save_state)
>                 return;
> @@ -784,6 +798,9 @@ void pci_restore_aspm_l1ss_state(struct pci_dev *dev)
>         if (!l1ss)
>                 return;
>
> +       if (skip_l1ss_restore)
> +               return;
> +
>         save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
>         if (!save_state)
>                 return;
> --
> 2.17.1
>