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

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Message-ID: <fnayczbumpynzvhafv3ryozlg2qwsxsyzpn5p44kc4o3hy7uux@lp5qgsd6ajtw>
Date: Sat, 8 Nov 2025 15:55:36 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: zhangsenchuan <zhangsenchuan@...incomputing.com>
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
Subject: Re: [PATCH 2/3] PCI: qcom: Check for the presence of a device
 instead of Link up during suspend

On Fri, Nov 07, 2025 at 02:27:15PM +0800, zhangsenchuan wrote:
> 
> 
> 
> > -----Original Messages-----
> > From: "Manivannan Sadhasivam" <mani@...nel.org>
> > Send time:Thursday, 06/11/2025 19:57:16
> > To: zhangsenchuan <zhangsenchuan@...incomputing.com>
> > 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
> > Subject: Re: [PATCH 2/3] PCI: qcom: Check for the presence of a device instead of Link up during suspend
> > 
> > On Thu, Nov 06, 2025 at 06:13:05PM +0800, zhangsenchuan wrote:
> > > 
> > > 
> > > 
> > > > -----Original Messages-----
> > > > From: "Manivannan Sadhasivam" <manivannan.sadhasivam@....qualcomm.com>
> > > > Send time:Thursday, 06/11/2025 14:13:25
> > > > To: lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org, bhelgaas@...gle.com
> > > > Cc: 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, "Manivannan Sadhasivam" <manivannan.sadhasivam@....qualcomm.com>
> > > > Subject: [PATCH 2/3] PCI: qcom: Check for the presence of a device instead of Link up during suspend
> > > > 
> > > > 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.
> > > > 
> > > > 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)) {
> > > 
> > > I'm a little confused.
> > > The pci_root_ports_have_device function can help check if there is any device 
> > > available under the Root Ports, if there is a device available, the resource 
> > > cannot be released, is it also necessary to release resources when entering 
> > > the L2/L3 state?
> > > 
> > 
> > It is upto the controller driver to decide. Once the link enters L2/L3, the
> > device will be in D3Cold state. So the controller can just disable all PCIe
> > resources to save power.
> > 
> > But it is not possible to transition all PCIe devices to D3Cold during suspend,
> > for instance NVMe. I'm hoping to fix it too in the coming days.
> > 
> Hi, Manivannan
> 
> Thank you for your explanation.
> 
> By the way, in v5 patch, I removed the dw_pcie_link_up judgment, and currently
> resources are directly released.
> At present, i have completed the pcie v5 patch without adding the 
> pci_root_ports_have_device function. Do I need to wait for you to merge it 
> before sending the V5 patch?
> 

I've merged my series to pci/controller/dwc branch. You can use this branch as a
base for your v5.

- Mani

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