linux-kernel - Re: [PATCH v4 1/2] PCI: dwc: Always stop link in the dw_pcie_suspend

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Message-ID: <20250114202622.GA483044@bhelgaas>
Date: Tue, 14 Jan 2025 14:26:22 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Richard Zhu <hongxing.zhu@....com>, dlemoal@...nel.org,
	jingoohan1@...il.com, bhelgaas@...gle.com, lpieralisi@...nel.org,
	kw@...ux.com, manivannan.sadhasivam@...aro.org, robh@...nel.org,
	quic_krichai@...cinc.com, imx@...ts.linux.dev,
	kernel@...gutronix.de, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] PCI: dwc: Always stop link in the
 dw_pcie_suspend_noirq

On Tue, Jan 14, 2025 at 02:32:38PM -0500, Frank Li wrote:
> On Tue, Jan 14, 2025 at 12:15:18PM -0600, Bjorn Helgaas wrote:
> > On Tue, Dec 10, 2024 at 04:15:56PM +0800, Richard Zhu wrote:
> > > On i.MX8QM, PCIe link can't be re-established again in
> > > dw_pcie_resume_noirq(), if the LTSSM_EN bit is not cleared properly in
> > > dw_pcie_suspend_noirq().
> > >
> > > Add dw_pcie_stop_link() into dw_pcie_suspend_noirq() to fix this issue and
> > > keep symmetric in suspend/resume function since there is
> > > dw_pcie_start_link() in dw_pcie_resume_noirq().
> > >
> > > Fixes: 4774faf854f5 ("PCI: dwc: Implement generic suspend/resume functionality")
> > > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > ---
> > >  drivers/pci/controller/dwc/pcie-designware-host.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > index f882b11fd7b94..f56cb7b9e6f99 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > @@ -1001,6 +1001,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> > >  		return ret;
> > >  	}
> > >
> > > +	dw_pcie_stop_link(pci);
> >
> > We should try to avoid changes to the generic DWC path just to
> > accommodate one controller.  Since other DWC-based controllers
> > apparently don't need dw_pcie_stop_link() here, this seems like it
> > might be the wrong place for this change.
> >
> > If doing dw_pcie_stop_link() here is really helpful for all DWC
> > controllers, this would be fine, but the commit log should then explain
> > why it helps everybody, not why one particular controller benefits.
> 
> It should be for all dwc controllers although find such problem at i.MX8QM
> platfrom. It should keep symmetric between suspend/resume function.
> 
> So far only layerscape and i.MX platform use these common functions. Other
> dwc platform still have not switched to this common function yet.

I see that layerscape uses dw_pcie_suspend_noirq():

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/dwc/pci-layerscape.c?id=v6.13-rc7#n379

But I don't see where imx6 does:

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/dwc/pci-imx6.c?id=v6.13-rc7#n1236

We don't currently have anything queued that touches pci-imx6.c; am I
missing a patch that converts pci-imx6.c to use
dw_pcie_suspend_noirq()?

This doesn't feel urgent yet since the commit log talks about i.MX8QM,
but I can't make a connection between i.MX8QM and this patch.

Bjorn