linux-kernel - RE: [PATCH v6 08/11] PCI: dwc: Invoke post_init in dw_pcie_resume

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Message-ID:
 <AS8PR04MB88334B71E559AC00907BDE028C82A@AS8PR04MB8833.eurprd04.prod.outlook.com>
Date: Fri, 9 Jan 2026 02:10:07 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Frank Li <frank.li@....com>, "l.stach@...gutronix.de"
	<l.stach@...gutronix.de>, "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"kwilczynski@...nel.org" <kwilczynski@...nel.org>, "mani@...nel.org"
	<mani@...nel.org>, "robh@...nel.org" <robh@...nel.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>, "shawnguo@...nel.org"
	<shawnguo@...nel.org>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>, "festevam@...il.com"
	<festevam@...il.com>, "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v6 08/11] PCI: dwc: Invoke post_init in
 dw_pcie_resume_noirq()

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@...nel.org>
> Sent: 2026年1月9日 5:50
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: Frank Li <frank.li@....com>; l.stach@...gutronix.de;
> lpieralisi@...nel.org; kwilczynski@...nel.org; mani@...nel.org;
> robh@...nel.org; krzk+dt@...nel.org; conor+dt@...nel.org;
> bhelgaas@...gle.com; shawnguo@...nel.org; s.hauer@...gutronix.de;
> kernel@...gutronix.de; festevam@...il.com; linux-pci@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org;
> imx@...ts.linux.dev; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v6 08/11] PCI: dwc: Invoke post_init in
> dw_pcie_resume_noirq()
> 
> On Wed, Oct 15, 2025 at 11:04:25AM +0800, Richard Zhu wrote:
> > If the ops has post_init callback, invoke it in dw_pcie_resume_noirq().
> 
> I'm trying to write the merge commit log for this branch, and I don't quite
> understand this.
> 
> The effect is to apply the GEN3_ZRXDC_NONCOMPL workaround for the
> ERR051586 erratum, and Mani added the hint that this enables REFCLK
> during resume.  But it seems weird that we apply a REFCLK workaround
> after the link is already up.
> 
> During probe, .post_init() is run after pci_host_probe(), so we apply the
> workaround after enumerating all the devices, which means REFCLK must
> already be valid and the link is already up.
> 
> Is "enabling REFCLK" actually what imx_pcie_host_post_init() does?
The codes are used to clean up the CLKREQ# override active low configurations
after link is up and the CLKREQ# is drove to low by remote endpoint device at
this point(support-clkreq is TRUE).
It paves the way to support the CLKREQ# toggling mandatory required by L1SS.

> 
> Could the workaround be done in imx_pcie_host_init() before the link is
> brought up?  If it could, it looks like we wouldn't need
> imx_pcie_host_post_init() at all.
> 
Two actions are done in imx_pcie_post_init().
One is to apply the workaround of ERR051586 by commit 744a1c20ce93 ("PCI:
imx6: Add workaround for errata ERR051586"). It should be applied after link
is up.
The other one is to clean up the CLKREQ# override active low configurations
previous set in imx_pcie_host_init().

Hope this can resolve your confusions.

Best Regards
Richard Zhu
> For now, I put this in the merge commit log:
> 
>   - Apply i.MX95 ERR051586 erratum workaround for REFCLK issue during
>     resume (Richard Zhu)
> 
> > ---
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 20c9333bcb1c4..2b59e7d2e6179 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -1199,6 +1199,9 @@ int dw_pcie_resume_noirq(struct dw_pcie *pci)
> >  	if (ret)
> >  		return ret;
> >
> > +	if (pci->pp.ops->post_init)
> > +		pci->pp.ops->post_init(&pci->pp);
> > +
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(dw_pcie_resume_noirq);
> > --
> > 2.37.1
> >