linux-kernel - Re: [PATCH v1] PCI: dwc: Clean up some unnecessary codes in dw_pcie_suspend

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Message-ID: <ZyzmBQlt5WJ+D9xM@lizhi-Precision-Tower-5810>
Date: Thu, 7 Nov 2024 11:08:37 -0500
From: Frank Li <Frank.li@....com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Richard Zhu <hongxing.zhu@....com>, jingoohan1@...il.com,
	bhelgaas@...gle.com, lpieralisi@...nel.org, kw@...ux.com,
	robh@...nel.org, imx@...ts.linux.dev, kernel@...gutronix.de,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] PCI: dwc: Clean up some unnecessary codes in
 dw_pcie_suspend_noirq()

On Thu, Nov 07, 2024 at 11:13:34AM +0000, Manivannan Sadhasivam wrote:
> On Thu, Nov 07, 2024 at 04:44:55PM +0800, Richard Zhu wrote:
> > Before sending PME_TURN_OFF, don't test the LTSSM stat. Since it's safe
> > to send PME_TURN_OFF message regardless of whether the link is up or
> > down. So, there would be no need to test the LTSSM stat before sending
> > PME_TURN_OFF message.
> >
>
> What is the incentive to send PME_Turn_Off when link is not up?

see Bjorn's comments in https://lore.kernel.org/imx/20241106222933.GA1543549@bhelgaas/

"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."

I think it may happen if EP device HOT remove/reset after if check.

Frank
>
> > Remove the L2 poll too, after the PME_TURN_OFF message is sent out.
> > Because the re-initialization would be done in dw_pcie_resume_noirq().
> >
>
> As Krishna explained, host needs to wait until the endpoint acks the message
> (just to give it some time to do cleanups). Then only the host can initiate
> D3Cold. It matters when the device supports L2.
>
> - Mani
>
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> >  .../pci/controller/dwc/pcie-designware-host.c | 20 ++++---------------
> >  1 file changed, 4 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index f86347452026..64c49adf81d2 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -917,7 +917,6 @@ static int dw_pcie_pme_turn_off(struct dw_pcie *pci)
> >  int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> >  {
> >  	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> > -	u32 val;
> >  	int ret = 0;
> >
> >  	/*
> > @@ -927,23 +926,12 @@ 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;
> >
> > -	/* Only send out PME_TURN_OFF when PCIE link is up */
> > -	if (dw_pcie_get_ltssm(pci) > DW_PCIE_LTSSM_DETECT_ACT) {
> > -		if (pci->pp.ops->pme_turn_off)
> > -			pci->pp.ops->pme_turn_off(&pci->pp);
> > -		else
> > -			ret = dw_pcie_pme_turn_off(pci);
> > -
> > +	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;
> > -
> > -		ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
> > -					PCIE_PME_TO_L2_TIMEOUT_US/10,
> > -					PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
> > -		if (ret) {
> > -			dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
> > -			return ret;
> > -		}
> >  	}
> >
> >  	dw_pcie_stop_link(pci);
> > --
> > 2.37.1
> >
>
> --
> மணிவண்ணன் சதாசிவம்