linux-kernel - Re: [PATCH] PCI/PM: Put devices to low power state on shutdown

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Message-ID: <20240911190516.GA644336@bhelgaas>
Date: Wed, 11 Sep 2024 14:05:16 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc: bhelgaas@...gle.com, mario.limonciello@....com,
	mika.westerberg@...ux.intel.com, linux-pci@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/PM: Put devices to low power state on shutdown

On Fri, Jul 12, 2024 at 02:24:11PM +0800, Kai-Heng Feng wrote:
> Some laptops wake up after poweroff when HP Thunderbolt Dock G4 is
> connected.
> 
> The following error message can be found during shutdown:
> pcieport 0000:00:1d.0: AER: Correctable error message received from 0000:09:04.0
> pcieport 0000:09:04.0: PCIe Bus Error: severity=Correctable, type=Data Link Layer, (Receiver ID)
> pcieport 0000:09:04.0:   device [8086:0b26] error status/mask=00000080/00002000
> pcieport 0000:09:04.0:    [ 7] BadDLLP
> 
> Calling aer_remove() during shutdown can quiesce the error message,
> however the spurious wakeup still happens.
> 
> The issue won't happen if the device is in D3 before system shutdown, so
> putting device to low power state before shutdown to solve the issue.
> 
> I don't have a sniffer so this is purely guesswork, however I believe
> putting device to low power state it's the right thing to do.

My objection here is that we don't have an explanation of why this
should matter or a pointer to any spec language about this situation,
so it feels a little bit random.

I suppose the problem wouldn't happen if AER interrupts were disabled?
We already do disable them in aer_suspend(), but maybe that's not used
in the shutdown path?

My understanding is that .shutdown() should turn off device interrupts
and stop DMA.  So maybe we need an aer_shutdown() that disables
interrupts?

> Link: https://bugzilla.kernel.org/show_bug.cgi?id=219036
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/pci/pci-driver.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index af2996d0d17f..4c6f66f3eb54 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -510,6 +510,14 @@ static void pci_device_shutdown(struct device *dev)
>  	if (drv && drv->shutdown)
>  		drv->shutdown(pci_dev);
>  
> +	/*
> +	 * If driver already changed device's power state, it can mean the
> +	 * wakeup setting is in place, or a workaround is used. Hence keep it
> +	 * as is.
> +	 */
> +	if (!kexec_in_progress && pci_dev->current_state == PCI_D0)
> +		pci_prepare_to_sleep(pci_dev);
> +
>  	/*
>  	 * If this is a kexec reboot, turn off Bus Master bit on the
>  	 * device to tell it to not continue to do DMA. Don't touch
> -- 
> 2.43.0
>