Re: [PATCH v1] PCI: imx6: Add force_suspend flag to override L1SS suspend skip

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Mar 18, 2026 at 02:55:45AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@kernel.org>
> ... [messed up quoting]

> > On Tue, Mar 17, 2026 at 02:12:56PM +0800, Richard Zhu wrote:
> > > Add a force_suspend flag to allow platform drivers to force the PCIe
> > > link into L2 state during suspend, even when L1SS (ASPM L1 Sub-States)
> > > is enabled.
> > >
> > > By default, the DesignWare PCIe host controller skips L2 suspend when
> > > L1SS is supported to meet low resume latency requirements for devices
> > > like NVMe. However, some platforms like i.MX PCIe need to enter L2
> > > state for proper power management regardless of L1SS support.
> > >
> > > Enable force_suspend for i.MX PCIe to ensure the link enters L2 during
> > > system suspend.
> > 
> > I'm a little bit skeptical about this.
> > 
> > What exactly does a "low resume latency requirement" mean?  Is
> > this an actual functional requirement that's special to NVMe, or
> > is it just the desire for low resume latency that everybody has
> > for all devices?
>
> From my understanding, L1SS mode is characterized by lower latency
> when compared to L2 or L3 modes.
>
> It can be used on all devices, avoiding frequent power on/off
> cycles. NVMe can also extend the service life of the equipment.

All the above applies to all platforms, so it's not an argument for
i.MX-specific code here.

> > Is there something special about i.MX here?  Why do we want i.MX
> > to be different from other host controllers?
>
> i.MX PCIe loses power supply during Deep Sleep Mode (DSM), requiring
> full reinitialization after system wake-up.

I don't know what DSM means in PCIe or how it would help justify this
change.

> Removing the L1SS check allows the suspend process to complete
> successfully and ensures the pci->suspended flag is set to true,
> which triggers the proper resume sequence during system wake-up for
> i.MX PCIes.

> > > Cc: stable@vger.kernel.org
> > > Fixes: 4774faf854f5 ("PCI: dwc: Implement generic suspend/resume
> > > functionality")
> > > Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> > > ---
> > >  drivers/pci/controller/dwc/pci-imx6.c             | 1 +
> > >  drivers/pci/controller/dwc/pcie-designware-host.c | 4 +++-
> > >  drivers/pci/controller/dwc/pcie-designware.h      | 1 +
> > >  3 files changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > > b/drivers/pci/controller/dwc/pci-imx6.c
> > > index 81a7093494c8..7902d39185a5 100644
> > > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > > @@ -1831,6 +1831,7 @@ static int imx_pcie_probe(struct platform_device
> > *pdev)
> > >  		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_SKIP_L23_READY))
> > >  			pci->pp.skip_l23_ready = true;
> > >  		pci->pp.use_atu_msg = true;
> > > +		pci->pp.force_l2_suspend = true;
> > >  		ret = dw_pcie_host_init(&pci->pp);
> > >  		if (ret < 0)
> > >  			return ret;
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > index a74339982c24..720154fd4ff0 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > @@ -1229,7 +1229,9 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> > >  	 * If L1SS is supported, then do not put the link into L2 as some
> > >  	 * devices such as NVMe expect low resume latency.
> > >  	 */
> > > -	if (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) &
> > PCI_EXP_LNKCTL_ASPM_L1)
> > > +	if (!pci->pp.force_l2_suspend &&
> > > +	    (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) &
> > > +	     PCI_EXP_LNKCTL_ASPM_L1))
> > >  		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 ae6389dd9caa..5261036bbe6e 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > @@ -447,6 +447,7 @@ struct dw_pcie_rp {
> > >  	bool			ecam_enabled;
> > >  	bool			native_ecam;
> > >  	bool                    skip_l23_ready;
> > > +	bool                    force_l2_suspend;
> > >  };
> > >
> > >  struct dw_pcie_ep_ops {
> > > --
> > > 2.37.1
> > >