linux-kernel - Re: [PATCH 1/2] net: wwan: iosm: Let PCI core handle PCI power transition

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Message-ID: <20211229201229.GA1698801@bhelgaas>
Date:   Wed, 29 Dec 2021 14:12:29 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     m.chetan.kumar@...el.com, linuxwwan@...el.com,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
        Loic Poulain <loic.poulain@...aro.org>,
        Sergey Ryazanov <ryazanov.s.a@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vaibhav Gupta <vaibhavgupta40@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH 1/2] net: wwan: iosm: Let PCI core handle PCI power
 transition

[+cc Rafael, in case you have insight about the PCI_D0 question below;
Vaibhav, since this is related to your generic PM conversions]

On Fri, Dec 24, 2021 at 04:19:13PM +0800, Kai-Heng Feng wrote:
> pci_pm_suspend_noirq() and pci_pm_resume_noirq() already handle power
> transition for system-wide suspend and resume, so it's not necessary to
> do it in the driver.

I see DaveM has already applied this, but it looks good to me, thanks
for doing this!

One minor question below...

> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/net/wwan/iosm/iosm_ipc_pcie.c | 49 ++-------------------------
>  1 file changed, 2 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/net/wwan/iosm/iosm_ipc_pcie.c b/drivers/net/wwan/iosm/iosm_ipc_pcie.c
> index 2fe88b8be3481..d73894e2a84ed 100644
> --- a/drivers/net/wwan/iosm/iosm_ipc_pcie.c
> +++ b/drivers/net/wwan/iosm/iosm_ipc_pcie.c
> @@ -363,67 +363,22 @@ static int __maybe_unused ipc_pcie_resume_s2idle(struct iosm_pcie *ipc_pcie)
>  
>  int __maybe_unused ipc_pcie_suspend(struct iosm_pcie *ipc_pcie)
>  {
> -	struct pci_dev *pdev;
> -	int ret;
> -
> -	pdev = ipc_pcie->pci;
> -
> -	/* Execute D3 one time. */
> -	if (pdev->current_state != PCI_D0) {
> -		dev_dbg(ipc_pcie->dev, "done for PM=%d", pdev->current_state);
> -		return 0;
> -	}

I don't understand the intent of this early exit, and it's not obvious
to me that pci_pm_suspend_noirq() bails out early when
(pdev->current_state != PCI_D0).

>  	/* The HAL shall ask the shared memory layer whether D3 is allowed. */
>  	ipc_imem_pm_suspend(ipc_pcie->imem);
>  
> -	/* Save the PCI configuration space of a device before suspending. */
> -	ret = pci_save_state(pdev);
> -
> -	if (ret) {
> -		dev_err(ipc_pcie->dev, "pci_save_state error=%d", ret);
> -		return ret;
> -	}
> -
> -	/* Set the power state of a PCI device.
> -	 * Transition a device to a new power state, using the device's PCI PM
> -	 * registers.
> -	 */
> -	ret = pci_set_power_state(pdev, PCI_D3cold);
> -
> -	if (ret) {
> -		dev_err(ipc_pcie->dev, "pci_set_power_state error=%d", ret);
> -		return ret;
> -	}
> -
>  	dev_dbg(ipc_pcie->dev, "SUSPEND done");
> -	return ret;
> +	return 0;
>  }
>  
>  int __maybe_unused ipc_pcie_resume(struct iosm_pcie *ipc_pcie)
>  {
> -	int ret;
> -
> -	/* Set the power state of a PCI device.
> -	 * Transition a device to a new power state, using the device's PCI PM
> -	 * registers.
> -	 */
> -	ret = pci_set_power_state(ipc_pcie->pci, PCI_D0);
> -
> -	if (ret) {
> -		dev_err(ipc_pcie->dev, "pci_set_power_state error=%d", ret);
> -		return ret;
> -	}
> -
> -	pci_restore_state(ipc_pcie->pci);
> -
>  	/* The HAL shall inform the shared memory layer that the device is
>  	 * active.
>  	 */
>  	ipc_imem_pm_resume(ipc_pcie->imem);
>  
>  	dev_dbg(ipc_pcie->dev, "RESUME done");
> -	return ret;
> +	return 0;
>  }
>  
>  static int __maybe_unused ipc_pcie_suspend_cb(struct device *dev)
> -- 
> 2.33.1
>