linux-kernel - Re: [PATCH v2 2/3] PCI: qcom: Check for the presence of a device instead of Link up during suspend

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Message-ID: <zgj3ubyb234ig6ndz6ov5q3szvuxnd3jkz2rjglbad4ksri6nl@ov7boxuar4va>
Date: Thu, 13 Nov 2025 22:24:17 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>, 
	lpieralisi@...nel.org, kwilczynski@...nel.org, bhelgaas@...gle.com, will@...nel.org, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, robh@...nel.org, 
	linux-arm-msm@...r.kernel.org, zhangsenchuan@...incomputing.com, vincent.guittot@...aro.org
Subject: Re: [PATCH v2 2/3] PCI: qcom: Check for the presence of a device
 instead of Link up during suspend

On Thu, Nov 13, 2025 at 10:41:47AM -0600, Bjorn Helgaas wrote:
> On Fri, Nov 07, 2025 at 10:13:18AM +0530, Manivannan Sadhasivam wrote:
> > The suspend handler checks for the PCIe Link up to decide when to turn off
> > the controller resources. But this check is racy as the PCIe Link can go
> > down just after this check.
> > 
> > So use the newly introduced API, pci_root_ports_have_device() that checks
> > for the presence of a device under any of the Root Ports to replace the
> > Link up check.
> 
> Why is pci_root_ports_have_device() itself not racy?
> 

Because it is very uncommon for the 'pci_dev' to go away during the host
controller suspend. It might still be possible in edge cases, but very common as
the link down. I can reword it.

- Mani

> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-qcom.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > index 805edbbfe7eb..b2b89e2e4916 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > @@ -2018,6 +2018,7 @@ static int qcom_pcie_probe(struct platform_device *pdev)
> >  static int qcom_pcie_suspend_noirq(struct device *dev)
> >  {
> >  	struct qcom_pcie *pcie;
> > +	struct dw_pcie_rp *pp;
> >  	int ret = 0;
> >  
> >  	pcie = dev_get_drvdata(dev);
> > @@ -2053,8 +2054,9 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
> >  	 * powerdown state. This will affect the lifetime of the storage devices
> >  	 * like NVMe.
> >  	 */
> > -	if (!dw_pcie_link_up(pcie->pci)) {
> > -		qcom_pcie_host_deinit(&pcie->pci->pp);
> > +	pp = &pcie->pci->pp;
> > +	if (!pci_root_ports_have_device(pp->bridge->bus)) {
> > +		qcom_pcie_host_deinit(pp);
> >  		pcie->suspended = true;
> >  	}
> >  
> > -- 
> > 2.48.1
> > 

-- 
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