[PATCH v1 1/4] PCI: dwc: Add quirk to fix hang issue in L2 poll of suspend

[Hongxing Zhu]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas at kernel.org>
> Sent: 2025年4月8日 22:59
> To: Hongxing Zhu <hongxing.zhu at nxp.com>
> Cc: jingoohan1 at gmail.com; Frank Li <frank.li at nxp.com>;
> l.stach at pengutronix.de; lpieralisi at kernel.org; kw at linux.com;
> manivannan.sadhasivam at linaro.org; robh at kernel.org;
> bhelgaas at google.com; shawnguo at kernel.org; s.hauer at pengutronix.de;
> kernel at pengutronix.de; festevam at gmail.com; linux-pci at vger.kernel.org;
> linux-arm-kernel at lists.infradead.org; imx at lists.linux.dev;
> linux-kernel at vger.kernel.org
> Subject: Re: [PATCH v1 1/4] PCI: dwc: Add quirk to fix hang issue in L2 poll of
> suspend
> 
> On Tue, Apr 08, 2025 at 02:52:18PM +0800, Richard Zhu wrote:
> > i.MX6QP PCIe is hang in L2 poll during suspend when one endpoint
> > device is connected, for example the Intel e1000e network card.
> >
> > Refer to Figure5-1 Link Power Management State Flow Diagram of PCI
> > Express Base Spec Rev6.0. L0 can be transferred to LDn directly.
> 
> Please include the section number.  Section numbers are easy to find
> because they're in the spec PDF contents, but figures are not.  E.g., "PCIe
> r6.0, sec 5.2, fig 5-1"
> 
Okay, would add them later.

> > It's harmless to let dw_pcie_suspend_noirq() proceed suspend after the
> > PME_Turn_Off is sent out, whatever the ltssm state is in L2 or L3 on
> > some PME_Turn_Off handshake broken platforms.
> 
> Maybe we don't need to poll for these LTSSM states on *any* platform, and
> we could just remove the poll and timeout completely?
> 
Yes, I used to suggest remove the L2 poll and timeout in the following
 discussion.
https://lkml.org/lkml/2024/11/18/200
Hi Krishna:
Is it feasible to eliminate the L2 poll and timeout in this context?

> If not, we need to explain why it is safe to skip the poll on some platforms.
> "Skipping the poll avoids a hang" is not a sufficient explanation.
> 
> s/ltssm/LTSSM/
Okay.
> 
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -947,7 +947,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)  {
> >  	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> >  	u32 val;
> > -	int ret;
> > +	int ret = 0;
> >
> >  	/*
> >  	 * If L1SS is supported, then do not put the link into L2 as some @@
> > -964,15 +964,17 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> >  			return ret;
> >  	}
> >
> > -	ret = read_poll_timeout(dw_pcie_get_ltssm, val,
> > -				val == DW_PCIE_LTSSM_L2_IDLE ||
> > -				val <= DW_PCIE_LTSSM_DETECT_WAIT,
> > -				PCIE_PME_TO_L2_TIMEOUT_US/10,
> > -				PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
> > -	if (ret) {
> > -		/* Only log message when LTSSM isn't in DETECT or POLL */
> > -		dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n",
> val);
> > -		return ret;
> > +	if (!dwc_check_quirk(pci, QUIRK_NOL2POLL_IN_PM)) {
> > +		ret = read_poll_timeout(dw_pcie_get_ltssm, val,
> > +					val == DW_PCIE_LTSSM_L2_IDLE ||
> > +					val <= DW_PCIE_LTSSM_DETECT_WAIT,
> > +					PCIE_PME_TO_L2_TIMEOUT_US/10,
> > +					PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
> > +		if (ret) {
> > +			/* Only log message when LTSSM isn't in DETECT or POLL */
> > +			dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM:
> 0x%x\n", val);
> > +			return ret;
> > +		}
> >  	}
> >
> >  	/*
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.h
> > b/drivers/pci/controller/dwc/pcie-designware.h
> > index 56aafdbcdaca..05fe654d7761 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -282,6 +282,9 @@
> >  /* Default eDMA LLP memory size */
> >  #define DMA_LLP_MEM_SIZE		PAGE_SIZE
> >
> > +#define QUIRK_NOL2POLL_IN_PM		BIT(0)
> > +#define dwc_check_quirk(pci, val)	(pci->quirk_flag & val)
> 
> Maybe just my personal preference, but I don't like things named "check"
> because that just means "look at"; it doesn't give any hint about how to
> interpret the result of looking at it.
> 
How about dwc_match_quirk(pci, val) (pci->quirk_flag & val)?

Best Regards
Richard Zhu
> >  struct dw_pcie;
> >  struct dw_pcie_rp;
> >  struct dw_pcie_ep;
> > @@ -491,6 +494,7 @@ struct dw_pcie {
> >  	const struct dw_pcie_ops *ops;
> >  	u32			version;
> >  	u32			type;
> > +	u32			quirk_flag;
> >  	unsigned long		caps;
> >  	int			num_lanes;
> >  	int			max_link_speed;
> > --
> > 2.37.1
> >