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

[mani@xxxxxxxxxx]

On Tue, Mar 24, 2026 at 02:01:58AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> > Sent: 2026年3月24日 6:09
> > To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> > Cc: Frank Li <frank.li@xxxxxxx>; jingoohan1@xxxxxxxxx;
> > 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; stable@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH v1] PCI: imx6: Add force_suspend flag to override L1SS
> > suspend skip
> > 
> > On Wed, Mar 18, 2026 at 02:55:45AM +0000, Hongxing Zhu wrote:
> > > > -----Original Message-----
> > > > From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> > > ... [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.
> >
> Hi Bjorn:
> Thanks for your kindly review. 
> Yes, it is.
> > > > 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.
> > 
> i.MX PCIe power is gated off during suspend, requiring full reinitialization
> on resume
> 

Is this an unconditional behavior? What if the PCIe device is configured as a
wakeup source like WOL, WOW? And if you connect NVMe, this behavior will result
in resume failure as NVMe driver expects the power to be retained if ASPM is
supported.

- Mani

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