netdev - Re: [PATCH 2/2] net: wwan: iosm: Keep device at D0 for s2idle case

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Date:   Wed, 29 Dec 2021 14:18:14 -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,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Vaibhav Gupta <vaibhavgupta40@...il.com>
Subject: Re: [PATCH 2/2] net: wwan: iosm: Keep device at D0 for s2idle case

[+cc Rafael, Vaibhav]

On Fri, Dec 24, 2021 at 04:19:14PM +0800, Kai-Heng Feng wrote:
> We are seeing spurious wakeup caused by Intel 7560 WWAN on AMD laptops.
> This prevent those laptops to stay in s2idle state.
> 
> From what I can understand, the intention of ipc_pcie_suspend() is to
> put the device to D3cold, and ipc_pcie_suspend_s2idle() is to keep the
> device at D0. However, the device can still be put to D3hot/D3cold by
> PCI core.
> 
> So explicitly let PCI core know this device should stay at D0, to solve
> the spurious wakeup.
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/net/wwan/iosm/iosm_ipc_pcie.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/wwan/iosm/iosm_ipc_pcie.c b/drivers/net/wwan/iosm/iosm_ipc_pcie.c
> index d73894e2a84ed..af1d0e837fe99 100644
> --- a/drivers/net/wwan/iosm/iosm_ipc_pcie.c
> +++ b/drivers/net/wwan/iosm/iosm_ipc_pcie.c
> @@ -340,6 +340,9 @@ static int __maybe_unused ipc_pcie_suspend_s2idle(struct iosm_pcie *ipc_pcie)
>  
>  	ipc_imem_pm_s2idle_sleep(ipc_pcie->imem, true);
>  
> +	/* Let PCI core know this device should stay at D0 */
> +	pci_save_state(ipc_pcie->pci);

This is a weird and non-obvious way to say "this device should stay at
D0".  It's also fairly expensive since pci_save_state() does a lot of
slow PCI config reads.

>  	return 0;
>  }
>  
> -- 
> 2.33.1
>