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Message-ID:
<AS8PR04MB8833589654705528BB7BA6648C32A@AS8PR04MB8833.eurprd04.prod.outlook.com>
Date: Thu, 21 Aug 2025 05:44:05 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Frank Li <frank.li@....com>, "jingoohan1@...il.com"
<jingoohan1@...il.com>, "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
"lpieralisi@...nel.org" <lpieralisi@...nel.org>, "kwilczynski@...nel.org"
<kwilczynski@...nel.org>, "mani@...nel.org" <mani@...nel.org>,
"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: [RESEND v3 1/5] PCI: dwc: Don't poll L2 if QUIRK_NOL2POLL_IN_PM
is existing in suspend
> -----Original Message-----
> From: Bjorn Helgaas <helgaas@...nel.org>
> Sent: 2025年8月20日 3:29
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: Frank Li <frank.li@....com>; jingoohan1@...il.com;
> l.stach@...gutronix.de; lpieralisi@...nel.org; kwilczynski@...nel.org;
> mani@...nel.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: [RESEND v3 1/5] PCI: dwc: Don't poll L2 if
> QUIRK_NOL2POLL_IN_PM is existing in suspend
>
> On Mon, Aug 18, 2025 at 03:32:01PM +0800, Richard Zhu wrote:
> > Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management State Flow
> > Diagram. Both L0 and L2/L3 Ready can be transferred to LDn directly.
> >
> > 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
> > after a recommended 10ms max wait refer to PCIe r6.0, sec 5.3.3.2.1
> > PME Synchronization.
> >
> > The LTSSM states are inaccessible on i.MX6QP and i.MX7D after the
> > PME_Turn_Off is sent out.
> >
> > To support this case, don't poll L2 state and apply a simple delay of
> > PCIE_PME_TO_L2_TIMEOUT_US(10ms) if the QUIRK_NOL2POLL_IN_PM flag
> is
> > set in suspend.
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > ---
> > .../pci/controller/dwc/pcie-designware-host.c | 31
> > +++++++++++++------ drivers/pci/controller/dwc/pcie-designware.h |
> > 4 +++
> > 2 files changed, 25 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 952f8594b5012..20a7f827babbf 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -1007,7 +1007,7 @@ 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;
>
> I think it's pointless to initialize "ret" because in every case where ret is set,
> we return it immediately if it is non-zero. We should just return 0 explicitly
> at the end of the function and skip this initialization.
>
You're right, thanks.
> > /*
> > * If L1SS is supported, then do not put the link into L2 as
> > some @@ -1024,15 +1024,26 @@ 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_quirk(pci, QUIRK_NOL2POLL_IN_PM)) {
> > + /*
> > + * Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management
> > + * State Flow Diagram. Both L0 and L2/L3 Ready can be
> > + * transferred to LDn directly. On the LTSSM states poll broken
> > + * platforms, add a max 10ms delay refer to PCIe r6.0,
> > + * sec 5.3.3.2.1 PME Synchronization.
>
> IIUC, the read_poll_timeout() below is waiting for the PME_TO_Ack
> responses to the PME_Turn_Off message.
>
> The Link state transition to L2/L3 Ready (or the subsequent L2, L3, or LDn
> states) is the indication that the downstream components have "performed
> any necessary local conditioning in preparation for power removal" and then
> responded with PME_TO_Ack.
>
> And the PCIE_PME_TO_L2_TIMEOUT_US timeout is the deadlock avoidance
> delay for cases where "one or more devices do not respond with a
> PME_TO_Ack".
>
> In the QUIRK_NOL2POLL_IN_PM case, I think the problem is that we can't
> *read* the LTSSM state to learn whether the Link transitioned to L2/L3
> Ready, L2, L3, or LDn. That wouldn't be surprising because per sec 5.2, "the
> LTSSM is typically powered by main power (not Vaux), so LTSSM will not be
> powered in either the L2 or the L3 state."
>
> I don't know what's different about i.MX6QP and i.MX7D. Maybe on most
> DWC platforms the LTSSM *is* powered in L2/L3/LDn, but on i.MX6QP and
> i.MX7D, it *isn't* powered in those states?
>
> If that's the case, we should say that somewhere here. And we should say
> what happens when we try to read the LTSSM when it's not powered.
> Does the read hang or cause some kind of error?
The read is hang directly, no any error messages are dumped.
How about add the following comments in the QUIRK_NOL2_POLL_IN_PM?
"Add the QUIRK_NOL2_POLL_IN_PM case to avoid the read hang, since LTSSM
might not be powered in L2/L3/LDn on some platforms. "
Best Regards
Richard Zhu
>
> > + */
> > + mdelay(PCIE_PME_TO_L2_TIMEOUT_US/1000);
> > + } else {
> > + 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 00f52d472dcdd..4e5bf6cb6ce80 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -295,6 +295,9 @@
> > /* Default eDMA LLP memory size */
> > #define DMA_LLP_MEM_SIZE PAGE_SIZE
> >
> > +#define QUIRK_NOL2POLL_IN_PM BIT(0)
> > +#define dwc_quirk(pci, val) (pci->quirk_flag & val)
> > +
> > struct dw_pcie;
> > struct dw_pcie_rp;
> > struct dw_pcie_ep;
> > @@ -504,6 +507,7 @@ 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
> >
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