[RESEND v3 4/5] PCI: dwc: Skip PME_Turn_Off message if there is no endpoint connected

[Hongxing Zhu]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas at kernel.org>
> Sent: 2025年8月20日 3:07
> To: Hongxing Zhu <hongxing.zhu at nxp.com>
> Cc: Frank Li <frank.li at nxp.com>; jingoohan1 at gmail.com;
> l.stach at pengutronix.de; lpieralisi at kernel.org; kwilczynski at kernel.org;
> mani at kernel.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: [RESEND v3 4/5] PCI: dwc: Skip PME_Turn_Off message if there is
> no endpoint connected
>
> On Mon, Aug 18, 2025 at 03:32:04PM +0800, Richard Zhu wrote:
> > Skip PME_Turn_Off message if there is no endpoint connected.
>
> What's the value of doing this?  Is this to make something faster?  If so,
> what and by how much?
>
> Or does it fix something that's currently broken?
>
> Seems like the discussion at
> https://lore.kern/
> el.org%2Flinux-pci%2F20241107084455.3623576-1-hongxing.zhu%40nxp.com%
> 2Ft%2F%23u&data=05%7C02%7Chongxing.zhu%40nxp.com%7Ced46fe10aeb74
> 21c88a508dddf53a24f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7
> C638912272493755203%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOn
> RydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%
> 3D%3D%7C0%7C%7C%7C&sdata=lIE7%2FlS5jiGxGPGVm5Hr5efpMbT19CLqrwu
> YNvAEdLY%3D&reserved=0
> might be relevant.
>
> This commit log only restates what the code does.  In my opinion we need
> actual justification for making this change.
Hi Bjorn:
Thanks for your comments.
This commit is mainly used to fix suspend/resume broken on i.MX7D PCIe.
A chip freeze is observed on i.MX7D when PCIe RC kicks off the PM_PME message
and no any devices are connected on the port.

Because i.MX7D is a very old design, and out of IP design technical support.
 I don't know what's going on inside the PCIe IP design when kick off the
 PM_PME message.

From SW perspective view, what I can do is to find out a quirk method to
 workaround this broken. Hope this can clear up your confusions.

Best Regards
Richard Zhu
>
> > Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
> > Reviewed-by: Frank Li <Frank.Li at nxp.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 15
> > +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 20a7f827babbf..868e7db4e3381 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -1016,12 +1016,15 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> >     if (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) &
> PCI_EXP_LNKCTL_ASPM_L1)
> >             return 0;
> >
> > -   if (pci->pp.ops->pme_turn_off) {
> > -           pci->pp.ops->pme_turn_off(&pci->pp);
> > -   } else {
> > -           ret = dw_pcie_pme_turn_off(pci);
> > -           if (ret)
> > -                   return ret;
> > +   /* Skip PME_Turn_Off message if there is no endpoint connected */
> > +   if (dw_pcie_get_ltssm(pci) > DW_PCIE_LTSSM_DETECT_WAIT) {
> > +           if (pci->pp.ops->pme_turn_off) {
> > +                   pci->pp.ops->pme_turn_off(&pci->pp);
> > +           } else {
> > +                   ret = dw_pcie_pme_turn_off(pci);
> > +                   if (ret)
> > +                           return ret;
> > +           }
> >     }
> >
> >     if (dwc_quirk(pci, QUIRK_NOL2POLL_IN_PM)) {
> > --
> > 2.37.1
> >