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

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Message-ID: <20220517150908.GA4528@thinkpad>
Date:   Tue, 17 May 2022 20:39:08 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.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 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.
> 

On SC7280, it is the Resource Power Manager(RPMh) that's powering the devices
down by cutting off the PCIe voltage domain. But the SC7280 RC driver itself
may put the PCIe devices into D3cold state during system suspend.
https://lore.kernel.org/lkml/CAE-0n53ho2DX2rqQMvvKAuDCfsWW62TceTaNPzv5Mn_NQ-U6dA@mail.gmail.com/T/

So to cover both cases (one is a hardware independent of SoC and another one is
the device driver), and to be generic, I've used the term "OS" after looking at
the previous flags.

Thanks,
Mani

> > 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
> > 

-- 
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