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

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Message-ID: <20241107163059.q64qebgwzn377fwb@thinkpad>
Date: Thu, 7 Nov 2024 16:30:59 +0000
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Frank Li <Frank.li@....com>
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 11:08:37AM -0500, Frank Li wrote:
> 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/
> 

Thanks for the pointer. Let me reply there itsef.

- Mani

> "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

-- 
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