RE: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with RC power loss

[Hongxing Zhu (OSS)]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> Sent: Thursday, July 30, 2026 6:30 AM
> To: Hongxing Zhu (OSS) <hongxing.zhu@xxxxxxxxxxx>
> Cc: Frank Li <frank.li@xxxxxxx>; l.stach@xxxxxxxxxxxxxx; lpieralisi@xxxxxxxxxx;
> kwilczynski@xxxxxxxxxx; mani@xxxxxxxxxx; robh@xxxxxxxxxx;
> bhelgaas@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx;
> festevam@xxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> Hongxing Zhu <hongxing.zhu@xxxxxxx>
> Subject: Re: [PATCH v2] PCI: dwc: Add suspend_poweroff flag for platforms with
> RC power loss
> 
> On Fri, Jul 17, 2026 at 03:41:21PM +0800, hongxing.zhu@xxxxxxxxxxx wrote:
> > From: Richard Zhu <hongxing.zhu@xxxxxxx>
> >
> > Some platforms like i.MX power off their PCIe RC controllers during
> > system suspend, requiring full re-initialization on resume. These
> > platforms need to enter L2 state to properly notify endpoints before
> > power loss.
> >
> > According to PCIe base spec r7.0, sec 5.2, the system software should
> > transition the device into D3Hot before broadcasting the PME_Turn_Off
> > message to initiate L2 entry. However, some endpoint devices fail the
> > D3cold capability check in pci_host_common_d3cold_possible(), which
> > would normally prevent L2 entry.
> 
> Wakeup devices that don't support PME from D3cold will fail the D3cold capability
> check, but I don't think those are the problem you're solving.
> 
You're right.

> This appears to handle devices that are not in D3hot, and that's not a property of
> the endpoint; it's a property of its driver.  Is the problem here that some driver
> didn't put its device in D3hot?
> 
I observed some endpoint devices failing the D3cold capability check, but I
haven't identified the root cause.

> > For platforms where the RC loses power during suspend, L2 entry is
> > essential regardless of D3cold support, as the link will be lost anyway.
> > Add a suspend_poweroff flag to force L2 entry in such cases, and
> > enable it for i.MX PCIe controllers.
> >
> > Note: This violates the spec requirement that devices be in D3Hot
> > before PME_Turn_Off, but is necessary for proper operation on
> > platforms with RC power loss during suspend.
> 
> If the device isn't in D3hot, it may still be active, and I think the PME_Turn_Off
> will abort any DMAs in progress, which doesn't sound like proper operation of the
> endpoint.
You're correct - this isn't ideal for endpoint operation. However, on i.MX
platforms, the RC controller will lose power during system suspend
regardless. Without sending PME_Turn_Off, endpoints would have no notification
before the link abruptly goes down.

This patch adds a flag to force L2 entry for such platforms, choosing to
notify endpoints (even if not ideal) rather than having the link drop
unexpectedly. I'm appreciated for suggestions if there's a better approach to
handle this scenario.

Thanks a lot.
Best Regards
Richard Zhu
> 
> > Signed-off-by: Richard Zhu <hongxing.zhu@xxxxxxx>
> > ---
> > Changes in v2:
> > - Rename the new added flag.
> > - Update commit description and comments.
> >
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c             | 11 +++++++++++
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++++++++--
> >  drivers/pci/controller/dwc/pcie-designware.h      |  8 ++++++++
> >  3 files changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 98e1db751132a..5a43bf396521b 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -1957,6 +1957,17 @@ static int imx_pcie_probe(struct platform_device
> *pdev)
> >  		 */
> >  		imx_pcie_add_lut_by_rid(imx_pcie, 0);
> >  	} else {
> > +		/*
> > +		 * i.MX RC is powered off during suspend, requiring L2 entry
> > +		 * to notify endpoints before power loss. Some endpoints fail
> > +		 * the D3cold capability check, which would normally prevent
> > +		 * L2 entry. Force L2 entry anyway since the link will be lost
> > +		 * when RC powers off.
> > +		 *
> > +		 * Note: Per PCIe spec r7.0 sec 5.2, devices should be in D3Hot
> > +		 * before PME_Turn_Off. This may not be guaranteed here.
> > +		 */
> > +		pci->pp.suspend_poweroff = true;
> >  		if (imx_check_flag(imx_pcie,
> IMX_PCIE_FLAG_SKIP_L23_READY))
> >  			pci->pp.skip_l23_ready = true;
> >  		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_KEEP_MSI_CAP))
> diff
> > --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 06722259d2e37..95a31d65e1ca9 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -1222,14 +1222,20 @@ static int dw_pcie_pme_turn_off(struct dw_pcie
> > *pci)
> >
> >  int dw_pcie_suspend_noirq(struct dw_pcie *pci)  {
> > -	bool pme_capable = false;
> > +	bool d3cold, pme_capable = false;
> >  	int ret = 0;
> >  	u32 val;
> >
> >  	if (!dw_pcie_link_up(pci))
> >  		goto stop_link;
> >
> > -	if (!pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable))
> > +	d3cold = pci_host_common_d3cold_possible(pci->pp.bridge,
> &pme_capable);
> > +	/*
> > +	 * Enter L2 if D3cold is possible, or if the platform loses RC power
> > +	 * during suspend (in which case L2 entry is required to notify
> > +	 * endpoints before power loss, regardless of D3cold support).
> > +	 */
> > +	if (!d3cold && !pci->pp.suspend_poweroff)
> >  		return 0;
> >
> >  	if (pci->pp.ops->pme_turn_off) {
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.h
> > b/drivers/pci/controller/dwc/pcie-designware.h
> > index de4b245b1758c..3ce7d30d9a4d5 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -471,6 +471,14 @@ struct dw_pcie_rp {
> >  	bool			native_ecam;
> >  	bool                    skip_l23_ready;
> >  	bool			skip_pwrctrl_off;
> > +	/*
> > +	 * suspend_poweroff: Force L2 entry during suspend even when D3cold
> > +	 * capability check fails. Used on platforms where RC loses power
> > +	 * during suspend and must notify endpoints via L2 entry before
> > +	 * power loss. May not meet PCIe spec requirement for devices to be
> > +	 * in D3Hot before PME_Turn_Off.
> > +	 */
> > +	bool                    suspend_poweroff;
> >  };
> >
> >  struct dw_pcie_ep_ops {
> > --
> > 2.34.1
> >