linux-kernel - Re: [PATCH 2/4] PCI/PTM: Enable PTM when restoring state

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Date:   Fri, 2 Sep 2022 10:25:54 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Rajvi Jingar <rajvi.jingar@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Cc:     Koba Ko <koba.ko@...onical.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "David E . Box" <david.e.box@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 2/4] PCI/PTM: Enable PTM when restoring state



On 9/2/22 7:58 AM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> The suspend path may disable PTM before saving config state, which means
> the PCI_PTM_CTRL_ENABLE bit in the saved state may be cleared even though
> we want PTM to be enabled when resuming.

If suspend is disabling PTM separately, why not enable it during the resume
operation? Why club it with PTM state restoration?

> 
> If "dev->ptm_enabled" is set, it means PTM should be enabled, so make sure
> PCI_PTM_CTRL_ENABLE is set when restoring the PTM state.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/pcie/ptm.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
> index b6a417247ce3..3115601a85ef 100644
> --- a/drivers/pci/pcie/ptm.c
> +++ b/drivers/pci/pcie/ptm.c
> @@ -82,6 +82,14 @@ void pci_restore_ptm_state(struct pci_dev *dev)
>  		return;
>  
>  	cap = (u16 *)&save_state->cap.data[0];
> +
> +	/*
> +	 * The suspend path may disable PTM before saving config state.
> +	 * Make sure PCI_PTM_CTRL_ENABLE is set if PTM should be enabled.
> +	 */
> +	if (dev->ptm_enabled)
> +		*cap |= PCI_PTM_CTRL_ENABLE;
> +
>  	pci_write_config_word(dev, ptm + PCI_PTM_CTRL, *cap);
>  }
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer