linux-kernel - RE: [PATCH v3] PCI: dwc: Clean up some unnecessary codes in dw_pcie_suspend

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Message-ID:
 <AS8PR04MB867676A6078A1DC792C16AB58C212@AS8PR04MB8676.eurprd04.prod.outlook.com>
Date: Wed, 20 Nov 2024 01:04:07 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: Frank Li <frank.li@....com>
CC: "jingoohan1@...il.com" <jingoohan1@...il.com>, "bhelgaas@...gle.com"
	<bhelgaas@...gle.com>, "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"kw@...ux.com" <kw@...ux.com>, "manivannan.sadhasivam@...aro.org"
	<manivannan.sadhasivam@...aro.org>, "robh@...nel.org" <robh@...nel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "kernel@...gutronix.de"
	<kernel@...gutronix.de>, "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3] PCI: dwc: Clean up some unnecessary codes in
 dw_pcie_suspend_noirq()

> -----Original Message-----
> From: Frank Li <frank.li@....com>
> Sent: 2024年11月20日 2:10
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: jingoohan1@...il.com; bhelgaas@...gle.com; lpieralisi@...nel.org;
> kw@...ux.com; manivannan.sadhasivam@...aro.org; robh@...nel.org;
> imx@...ts.linux.dev; kernel@...gutronix.de; linux-pci@...r.kernel.org;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v3] PCI: dwc: Clean up some unnecessary codes in
> dw_pcie_suspend_noirq()
> 
> On Mon, Nov 18, 2024 at 01:44:47PM +0800, Richard Zhu wrote:
> > Before sending PME_TURN_OFF, don't test the LTSSM state. 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 state before
> > sending PME_TURN_OFF message.
> >
> > Only print the message when ltssm_stat is not in DETECT and POLL.
> > In the other words, there isn't an error message when no endpoint is
> > connected at all.
> >
> > Also, when the endpoint is connected and PME_TURN_OFF is sent, do not
> > return error if the link doesn't enter L2. Just print a warning and
> > continue with the suspend as the link will be recovered in
> dw_pcie_resume_noirq().
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> > v3 changes:
> > - Refine the commit message refer to Manivannan's comments.
> > - Regarding Frank's comments, avoid 10ms wait when no link up.
> > v2 changes:
> > - Don't remove L2 poll check.
> > - Add one 1us delay after L2 entry.
> > - No error return when L2 entry is timeout
> > - Don't print message when no link up.
> > ---
> >  .../pci/controller/dwc/pcie-designware-host.c | 40
> > ++++++++++---------  drivers/pci/controller/dwc/pcie-designware.h  |
> > 1 +
> >  2 files changed, 23 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 24e89b66b772..68fbc16199e8 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -927,24 +927,28 @@ 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 (ret)
> > -			return ret;
> > +	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;
> > -		}
> > -	}
> > +	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 && (val > DW_PCIE_LTSSM_DETECT_WAIT))
> 
> if true of (val <= DW_PCIE_LTSSM_DETECT_WAIT), which means not device
> attached, 'ret' should be 0.
> 
> when ret is not 0, means, link up and not in L2 idle status. So check '(val >
> DW_PCIE_LTSSM_DETECT_WAIT)' is redundant.
> 
> NOT(val == DW_PCIE_LTSSM_L2_IDLE || val <=
> DW_PCIE_LTSSM_DETECT_WAIT) equal (val != DW_PCIE_LTSSM_L2_IDLE) &&
> (val > DW_PCIE_LTSSM_DETECT_WAIT)
I see. So only do the ret value check "if (ret)" is enough.
When ret is not 0, link is up, something is wrong in L2 entry, a warning would
 be printed. If ret is 0, that means L2 entry is done, or no link up at all.
Thanks.

Best Regards
Richard Zhu
> 
> Frank
> 
> > +		/* Only dump message when ltssm_stat isn't in DETECT and POLL */
> > +		dev_warn(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n",
> val);
> > +	else
> > +		/*
> > +		 * Refer to r6.0, sec 5.3.3.2.1, software should wait at least
> > +		 * 100ns after L2/L3 Ready before turning off refclock and
> > +		 * main power. It's harmless too when no endpoint connected.
> > +		 */
> > +		udelay(1);
> >
> >  	dw_pcie_stop_link(pci);
> >  	if (pci->pp.ops->deinit)
> > @@ -952,7 +956,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> >
> >  	pci->suspended = true;
> >
> > -	return ret;
> > +	return 0;
> >  }
> >  EXPORT_SYMBOL_GPL(dw_pcie_suspend_noirq);
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.h
> > b/drivers/pci/controller/dwc/pcie-designware.h
> > index 347ab74ac35a..bf036e66717e 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -330,6 +330,7 @@ enum dw_pcie_ltssm {
> >  	/* Need to align with PCIE_PORT_DEBUG0 bits 0:5 */
> >  	DW_PCIE_LTSSM_DETECT_QUIET = 0x0,
> >  	DW_PCIE_LTSSM_DETECT_ACT = 0x1,
> > +	DW_PCIE_LTSSM_DETECT_WAIT = 0x6,
> >  	DW_PCIE_LTSSM_L0 = 0x11,
> >  	DW_PCIE_LTSSM_L2_IDLE = 0x15,
> >
> > --
> > 2.37.1
> >