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

[Bjorn Helgaas <helgaas@kernel.org>]

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?

Is there something special about i.MX here?  Why do we want i.MX to be
different from other host controllers?

> 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
>