On Wed, Nov 06, 2024 at 01:59:41AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> > Sent: 2024年11月6日 7:27
> > To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> > Cc: kwilczynski@xxxxxxxxxx; bhelgaas@xxxxxxxxxx;
> > lorenzo.pieralisi@xxxxxxx; Frank Li <frank.li@xxxxxxx>; mani@xxxxxxxxxx;
> > linux-pci@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH v2] PCI: dwc: Fix resume failure if no EP is connected at
> > some platforms
> >
> > On Mon, Jul 22, 2024 at 02:15:13PM +0800, Richard Zhu wrote:
> > > The dw_pcie_suspend_noirq() function currently returns success
> > > directly if no endpoint (EP) device is connected. However, on some
> > > platforms, power loss occurs during suspend, causing dw_resume() to do
> > > nothing in this case.
> > > This results in a system halt because the DWC controller is not
> > > initialized after power-on during resume.
> > > @@ -933,23 +933,23 @@ 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 (dw_pcie_get_ltssm(pci) <= DW_PCIE_LTSSM_DETECT_ACT)
> > > - 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 (dw_pcie_get_ltssm(pci) > DW_PCIE_LTSSM_DETECT_ACT) {
> > > + /* Only send out PME_TURN_OFF when PCIE link is up */
> > > + if (pci->pp.ops->pme_turn_off)
> > > + pci->pp.ops->pme_turn_off(&pci->pp);
> > > + else
> > > + ret = dw_pcie_pme_turn_off(pci);
> >
> > This looks possibly racy since the link can go down at any point.
>
> When link is down and without this commit changes,
> dw_pcie_suspend_noirq() return directly, and the PME_TURN_OFF
> wouldn't be kicked off.
Right, that's the code change.
> I change the behavior to issue the PME_TURN_OFF when link is up
> here.
But I don't think you responded to the race question. What happens
here?
if (dw_pcie_get_ltssm(pci) > DW_PCIE_LTSSM_DETECT_ACT) {
--> link goes down here <--
pci->pp.ops->pme_turn_off(&pci->pp);
You decide the LTSSM is active and the link is up. Then the link goes
down. Then you send PME_Turn_off. Now what?
If it's safe to try to send PME_Turn_off regardless of whether the
link is up or down, there would be no need to test the LTSSM state.
Bjorn
