linux-kernel - Re: [PATCH 1/3] PCI: Add a flag to notify PCI drivers about powerdown during suspend

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Message-ID: <20220516201817.GA1047280@bhelgaas>
Date:   Mon, 16 May 2022 15:18:17 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     bhelgaas@...gle.com, lorenzo.pieralisi@....com, kbusch@...nel.org,
        hch@....de, linux-nvme@...ts.infradead.org,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, svarbanov@...sol.com,
        bjorn.andersson@...aro.org, axboe@...com,
        quic_vbadigan@...cinc.com, quic_krichai@...cinc.com,
        quic_nitirawa@...cinc.com, vidyas@...dia.com, sagi@...mberg.me
Subject: Re: [PATCH 1/3] PCI: Add a flag to notify PCI drivers about
 powerdown during suspend

On Fri, May 13, 2022 at 04:30:25PM +0530, Manivannan Sadhasivam wrote:
> On some systems like Chromebooks based on Qcom chipsets, the OS may
> powerdown all PCIe devices during system suspend for aggressive
> powersaving. In that case, the PCI host controller drivers need to notify
> the PCI device drivers that the power will be taken off during system
> suspend so that the drivers can prepare the devices accordingly.

"The OS may powerdown all PCIe devices ..." makes it sound like this
is an OS policy decision.  Where exactly (what function) is that?

Or if it's not an OS policy decision, but rather some property of the
hardware, say that specifically.

> One prime example is the PCI NVMe driver. This flag can be used by the
> driver to shutdown the NVMe device during suspend and recover it during
> resume.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  include/linux/pci.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 60adf42460ab..069caf1fe88d 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -578,6 +578,7 @@ struct pci_host_bridge {
>  	unsigned int	preserve_config:1;	/* Preserve FW resource setup */
>  	unsigned int	size_windows:1;		/* Enable root bus sizing */
>  	unsigned int	msi_domain:1;		/* Bridge wants MSI domain */
> +	unsigned int	suspend_poweroff:1;	/* OS may poweroff devices during system suspend */
>  
>  	/* Resource alignment requirements */
>  	resource_size_t (*align_resource)(struct pci_dev *dev,
> -- 
> 2.25.1
>