linux-kernel - Re: [PATCH 2/2] PCI/PM: Fix pci_pm_suspend

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Message-ID: <7d5de631-3ebc-01ee-69b8-ae105408cb59@intel.com>
Date:   Fri, 11 Mar 2022 19:38:15 +0100
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Rajvi Jingar <rajvi.jingar@...el.com>, <bhelgaas@...gle.com>
CC:     <david.e.box@...ux.intel.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] PCI/PM: Fix pci_pm_suspend_noirq() to disable PTM

On 2/24/2022 9:29 PM, Rajvi Jingar wrote:
> For the PCIe devices (like nvme) that do not go into D3 state still need to
> disable PTM on PCIe root ports to allow the port to enter a lower-power PM
> state and the SoC to reach a lower-power idle state as a whole. Move the
> pci_disable_ptm() out of pci_prepare_to_sleep() as this code path is not
> followed for devices that do not go into D3. This patch fixes the issue
> seen on Dell XPS 9300 with Ice Lake CPU and Dell Precision 5530 with Coffee
> Lake CPU platforms to get improved residency in low power idle states.
>
> Signed-off-by: Rajvi Jingar <rajvi.jingar@...el.com>
> Suggested-by: David E. Box <david.e.box@...ux.intel.com>

I would add a Fixes tag pointing to the commit that introduced 
pci_disable_ptm().

Otherwise I agree with this change:

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>


> ---
>   drivers/pci/pci-driver.c | 11 +++++++++++
>   drivers/pci/pci.c        | 10 ----------
>   2 files changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index ac3f7e1676a9..8be3f81afdf6 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -836,6 +836,17 @@ static int pci_pm_suspend_noirq(struct device *dev)
>   
>   	if (!pci_dev->state_saved) {
>   		pci_save_state(pci_dev);
> +
> +		/*
> +		 * There are systems (for example, Intel mobile chips since Coffee
> +		 * Lake) where the power drawn while suspended can be significantly
> +		 * reduced by disabling PTM on PCIe root ports as this allows the
> +		 * port to enter a lower-power PM state and the SoC to reach a
> +		 * lower-power idle state as a whole.
> +		 */
> +		if (pci_pcie_type(pci_dev) == PCI_EXP_TYPE_ROOT_PORT)
> +			pci_disable_ptm(pci_dev);
> +
>   		if (!pci_dev->skip_bus_pm && pci_power_manageable(pci_dev))
>   			pci_prepare_to_sleep(pci_dev);
>   	}
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 9ecce435fb3f..f8768672c064 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2660,16 +2660,6 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
>   	if (target_state == PCI_POWER_ERROR)
>   		return -EIO;
>   
> -	/*
> -	 * There are systems (for example, Intel mobile chips since Coffee
> -	 * Lake) where the power drawn while suspended can be significantly
> -	 * reduced by disabling PTM on PCIe root ports as this allows the
> -	 * port to enter a lower-power PM state and the SoC to reach a
> -	 * lower-power idle state as a whole.
> -	 */
> -	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> -		pci_disable_ptm(dev);
> -
>   	pci_enable_wake(dev, target_state, wakeup);
>   
>   	error = pci_set_power_state(dev, target_state);