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Subject: Re: [PATCH] PCI: Save/restore L1 PM Substate extended capability
 registers
To:     "David E. Box" <david.e.box@linux.intel.com>,
        <bhelgaas@google.com>, <rafael@kernel.org>
CC:     <linux-pci@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20201208220624.21877-1-david.e.box@linux.intel.com>
From:   Vidya Sagar <vidyas@nvidia.com>
Message-ID: <d7708556-40b5-c66c-d0c7-ccfe9999691c@nvidia.com>
Date:   Wed, 9 Dec 2020 09:38:00 +0530
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There is a change already available for it in linux-next
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=4257f7e008ea394fcecc050f1569c3503b8bcc15

Thanks,
Vidya Sagar

On 12/9/2020 3:36 AM, David E. Box wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Intel systems that support ACPI Low Power Idle it has been observed
> that the L1 Substate capability can return disabled after a s2idle
> cycle. This causes the loss of L1 Substate support during runtime
> leading to higher power consumption. Add save/restore of the L1SS
> control registers.
> 
> Signed-off-by: David E. Box <david.e.box@linux.intel.com>
> ---
>   drivers/pci/pci.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 49 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e578d34095e9..beee3d9952a6 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1539,6 +1539,48 @@ static void pci_restore_ltr_state(struct pci_dev *dev)
>          pci_write_config_word(dev, ltr + PCI_LTR_MAX_NOSNOOP_LAT, *cap++);
>   }
> 
> +static void pci_save_l1ss_state(struct pci_dev *dev)
> +{
> +       int l1ss;
> +       struct pci_cap_saved_state *save_state;
> +       u16 *cap;
> +
> +       if (!pci_is_pcie(dev))
> +               return;
> +
> +       l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> +       if (!l1ss)
> +               return;
> +
> +       save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
> +       if (!save_state) {
> +               pci_err(dev, "no suspend buffer for L1 Substates\n");
> +               return;
> +       }
> +
> +       cap = (u16 *)&save_state->cap.data[0];
> +       pci_read_config_word(dev, l1ss + PCI_L1SS_CTL1, cap++);
> +       pci_read_config_word(dev, l1ss + PCI_L1SS_CTL1 + 2, cap++);
> +       pci_read_config_word(dev, l1ss + PCI_L1SS_CTL2, cap++);
> +}
> +
> +static void pci_restore_l1ss_state(struct pci_dev *dev)
> +{
> +       struct pci_cap_saved_state *save_state;
> +       int l1ss;
> +       u16 *cap;
> +
> +       save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
> +       l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> +       if (!save_state || !l1ss)
> +               return;
> +
> +       cap = (u16 *)&save_state->cap.data[0];
> +       pci_write_config_word(dev, l1ss + PCI_L1SS_CTL1, *cap++);
> +       pci_write_config_word(dev, l1ss + PCI_L1SS_CTL1 + 2, *cap++);
> +       pci_write_config_word(dev, l1ss + PCI_L1SS_CTL2, *cap++);
> +}
> +
>   /**
>    * pci_save_state - save the PCI configuration space of a device before
>    *                 suspending
> @@ -1563,6 +1605,7 @@ int pci_save_state(struct pci_dev *dev)
>          if (i != 0)
>                  return i;
> 
> +       pci_save_l1ss_state(dev);
>          pci_save_ltr_state(dev);
>          pci_save_dpc_state(dev);
>          pci_save_aer_state(dev);
> @@ -1670,6 +1713,7 @@ void pci_restore_state(struct pci_dev *dev)
>           */
>          pci_restore_ltr_state(dev);
> 
> +       pci_restore_l1ss_state(dev);
>          pci_restore_pcie_state(dev);
>          pci_restore_pasid_state(dev);
>          pci_restore_pri_state(dev);
> @@ -3332,6 +3376,11 @@ void pci_allocate_cap_save_buffers(struct pci_dev *dev)
>          if (error)
>                  pci_err(dev, "unable to allocate suspend buffer for LTR\n");
> 
> +       error = pci_add_ext_cap_save_buffer(dev, PCI_EXT_CAP_ID_L1SS,
> +                                           3 * sizeof(u16));
> +       if (error)
> +               pci_err(dev, "unable to allocate suspend buffer for L1 Substates\n");
> +
>          pci_allocate_vc_save_buffers(dev);
>   }
> 
> --
> 2.20.1
>