RE: [PATCH v1] PCI: dwc: Add force_l2 flag for platforms requiring L2 entry without D3cold

[Hongxing Zhu (OSS)]

> -----Original Message-----
> From: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> Sent: Thursday, July 16, 2026 12:57 AM
> To: Hongxing Zhu (OSS) <hongxing.zhu@xxxxxxxxxxx>
> Cc: Frank Li <frank.li@xxxxxxx>; jingoohan1@xxxxxxxxx;
> l.stach@xxxxxxxxxxxxxx; lpieralisi@xxxxxxxxxx; kwilczynski@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 v1] PCI: dwc: Add force_l2 flag for platforms requiring L2
> entry without D3cold
> 
> On Mon, Jul 06, 2026 at 10:47:52AM +0800, hongxing.zhu@xxxxxxxxxxx wrote:
> > From: Richard Zhu <hongxing.zhu@xxxxxxx>
> >
> > Some platforms like i.MX have their PCIe RC controllers powered off
> > during system suspend, requiring full re-initialization on resume.
> > These platforms need to enter L2 state to properly notify endpoints
> > before power loss, even when D3cold is not supported.
> >
> 
> So during suspend, RC goes down but the EP stays powered ON? And due to RC
> suddenly going down, EP is observing LDn?
>
In general, the EP enters D3 state before the RC goes down. Then when the RC
powers down, the EP is powered off and observes LDn.

However, I have also observed that some EP devices return false in
pci_host_common_d3cold_possible(). That's why I added this flag.

> Can you control RC power during suspend from pci-imx6 driver? I guess not.
> 
That's correct.

> Also, is this behavior applicable to all i.MX6 platforms? If so, how the suspend
> worked before?
Yes, this behavior applies to all i.MX platforms.

> 
> > Add a force_l2 flag to allow platform drivers to request L2 entry
> > during suspend regardless of D3cold capability, and enable it for i.MX
> > PCIe controllers.
> >
> 
> PCIe base spec r7.0, sec 5.2, mentions that the system software should transition
> the device into D3Hot before broadcasing the PME_Turn_Off message.
> So here we'd be violating that section of the spec if the endpoint is in non-D3Hot
> state.
> 
> But honestly, I don't have a better solution than intiating L2 entry sequence
> forcefully. Atleast, it should be documented in the comments and patch
> description.
Agreed. I will add this clarification to both the comments and patch
description.

> 
> > Signed-off-by: Richard Zhu <hongxing.zhu@xxxxxxx>
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c             | 5 +++++
> >  drivers/pci/controller/dwc/pcie-designware-host.c | 8 ++++++--
> >  drivers/pci/controller/dwc/pcie-designware.h      | 5 +++++
> >  3 files changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index f55a68f60eea9..ea0b4eb03c1d0 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -1966,6 +1966,11 @@ 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, force L2 entry to
> > +		 * ensure proper endpoint notification before power loss.
> > +		 */
> > +		pci->pp.force_l2 = 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..e3f022d2d453a 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -1222,14 +1222,18 @@ 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 platform requires forced L2 entry
> > +	 */
> > +	if (!d3cold && !pci->pp.force_l2)
> >  		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..5e88459e0cfa0 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -471,6 +471,11 @@ struct dw_pcie_rp {
> >  	bool			native_ecam;
> >  	bool                    skip_l23_ready;
> >  	bool			skip_pwrctrl_off;
> > +	/*
> > +	 * Force L2 entry even if D3cold not possible (e.g., when RC loses
> > +	 * power).
> > +	 */
> > +	bool                    force_l2;
> 
> Can it be called, 'suspend_poweroff' to indicate the actual quirk?
Good suggestion. I will rename it to 'suspend_poweroff'.

Best Regards
Richard Zhu
> 
> - Mani
> 
> --
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