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

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Message-ID: <tv67nul5owjqywhqmekb2cf5q2acyb3jpcfvz6k62jd6sxd5gv@izy7uomaakei>
Date: Sat, 31 May 2025 23:17:13 +0530
From: 
	"manivannan.sadhasivam@...aro.org" <manivannan.sadhasivam@...aro.org>
To: Hongxing Zhu <hongxing.zhu@....com>
Cc: Bjorn Helgaas <helgaas@...nel.org>, 
	Krishna Chaitanya Chundru <quic_krichai@...cinc.com>, "jingoohan1@...il.com" <jingoohan1@...il.com>, 
	Frank Li <frank.li@....com>, "l.stach@...gutronix.de" <l.stach@...gutronix.de>, 
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>, "kw@...ux.com" <kw@...ux.com>, 
	"robh@...nel.org" <robh@...nel.org>, "bhelgaas@...gle.com" <bhelgaas@...gle.com>, 
	"shawnguo@...nel.org" <shawnguo@...nel.org>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>, 
	"kernel@...gutronix.de" <kernel@...gutronix.de>, "festevam@...il.com" <festevam@...il.com>, 
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/4] PCI: dwc: Add quirk to fix hang issue in L2 poll
 of suspend

On Wed, Apr 09, 2025 at 02:31:22AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@...nel.org>
> > Sent: 2025年4月8日 22:59
> > To: Hongxing Zhu <hongxing.zhu@....com>
> > Cc: jingoohan1@...il.com; Frank Li <frank.li@....com>;
> > l.stach@...gutronix.de; lpieralisi@...nel.org; kw@...ux.com;
> > manivannan.sadhasivam@...aro.org; robh@...nel.org;
> > bhelgaas@...gle.com; shawnguo@...nel.org; s.hauer@...gutronix.de;
> > kernel@...gutronix.de; festevam@...il.com; linux-pci@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org; imx@...ts.linux.dev;
> > linux-kernel@...r.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?
> 

Spec r6.0, sec 5.2 mandates L2/L3 Ready state:

"L2/L3 Ready transition protocol support is required."

Also in many places, it suggests waiting for L2/L3 Ready state before powering
down the device. So I don't think we should just remove the poll for all
platforms.

> > 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.
> > 

So the issue is that the device doesn't transition to L2/L3 Ready state and the
host platform just 'hangs'? Do we know why the hang happens?

> > 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)?
> 

Maybe just dwc_quirk()?

- Mani

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