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

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Date:   Thu, 26 May 2022 15:48:37 -0500
From:   Rob Herring <robh@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        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 Mon, May 16, 2022 at 03:18:17PM -0500, Bjorn Helgaas wrote:
> 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 */

Why does this apply to the whole host bridge? What if you have multiple 
devices and some are powered off and others aren't?

Rob