linux-kernel - Re: [PATCH v2 3/3] PCI: dwc: Check for the device presence during suspend and resume

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Message-ID: <6uidenlpio4lsn7cecdubxlojo4slm6g76zteu74jg7xqhnv2y@kmsnhuh3dqiz>
Date: Thu, 13 Nov 2025 22:31:27 +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, 
	Frank Li <Frank.li@....com>
Subject: Re: [PATCH v2 3/3] PCI: dwc: Check for the device presence during
 suspend and resume

On Thu, Nov 13, 2025 at 10:40:13AM -0600, Bjorn Helgaas wrote:
> [+cc Frank]
> 
> On Fri, Nov 07, 2025 at 10:13:19AM +0530, Manivannan Sadhasivam wrote:
> > If there is no device available under the Root Ports, there is no point in
> > sending PME_Turn_Off and waiting for L2/L3 transition during suspend, it
> > will result in a timeout. Hence, skip those steps if no device is available
> > during suspend.
> > 
> > During resume, do not wait for the link up if there was no device connected
> > before suspend. It is very unlikely that a device will get connected while
> > the host system was suspended.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 20c9333bcb1c..5a39e7139ec9 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -20,6 +20,7 @@
> >  #include <linux/platform_device.h>
> >  
> >  #include "../../pci.h"
> > +#include "../pci-host-common.h"
> >  #include "pcie-designware.h"
> >  
> >  static struct pci_ops dw_pcie_ops;
> > @@ -1129,6 +1130,9 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> >  	u32 val;
> >  	int ret;
> >  
> > +	if (!pci_root_ports_have_device(pci->pp.bridge->bus))
> > +		goto stop_link;
> 
> This looks racy.  Maybe it's still OK, but I think it would be good to
> include a comment to acknowledge that and explain why either outcome
> is acceptable, e.g., if a user removes a device during suspend, it
> results in a timeout but nothing more terrible.
> 

Ok.

> >  	/*
> >  	 * If L1SS is supported, then do not put the link into L2 as some
> >  	 * devices such as NVMe expect low resume latency.
> > @@ -1162,6 +1166,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> >  	 */
> >  	udelay(1);
> >  
> > +stop_link:
> >  	dw_pcie_stop_link(pci);
> >  	if (pci->pp.ops->deinit)
> >  		pci->pp.ops->deinit(&pci->pp);
> > @@ -1195,6 +1200,14 @@ int dw_pcie_resume_noirq(struct dw_pcie *pci)
> >  	if (ret)
> >  		return ret;
> >  
> > +	/*
> > +	 * If there was no device before suspend, skip waiting for link up as
> > +	 * it is bound to fail. It is very unlikely that a device will get
> > +	 * connected *during* suspend.
> 
> I'm not convinced.  Unlike the suspend side, where the race window is
> tiny, here the window is the entire time the system is suspended, and
> at least in laptop usage, there's no reason I would hesitate to plug
> something in while suspended.
> 

In that case, we just need to do:

	/* Ignore errors as there could be no devices connected */
	dw_pcie_wait_for_link()

I wanted to avoid the timeout if we knew that there was no device connected
during suspend.

- Mani

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