Re: [PATCH v3] PCI: imx6: Enable ASPM L1 only iff CLKREQ# is supported

[Krishna Chaitanya Chundru]

On 8/28/2026 6:40 PM, Michal Gorlas wrote:
> Since commit f3ac2ff14834 ("PCI/ASPM: Enable all ClockPM and ASPM
> states for devicetree platforms"), ASPM states are force enabled
> on all devicetree platforms. This causes PCI devices on some i.MX SoCs
> (for e.g. i.MX 8M Plus Kontron SMARC eval carrier) to enter L1 even
> though CLKREQ# is not supported (and consequently supports-clkreq is
> not set in pcie controller node of their DT), which causes the device to
> never wake up from L1.
CLKREQ pin will not play any role  in entry and exit L1, it will be used only for
L1 sub states entry and exit.

If you want to disable L1, try to add aspm-no-l1 property in root port[1].
Recently aspm driver change was merged which will disable L1 if that property
is present[2]

[1]: dt-schema/dtschema/schemas/pci/pci-bus-common.yaml at main ·
devicetree-org/dt-schema
<https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/pci/pci-bus-common.yaml#L167>
[2]: Re: [PATCH v6 0/3] PCI/ASPM: Mask ASPM states based on Devicetree
properties - Bjorn Helgaas
<https://lore.kernel.org/all/20260812023735.GA846004@bhelgaas/>

- Krishna Chaitanya.
>
> Hence, disable L1 capability in the LNKCAP register if supports-clkreq
> is not set in the DT explicitly. For devices that set
> IMX_PCIE_FLAG_BROKEN_SUSPEND, disable L1 on resume as well, as these
> skip imx_pcie_host_init().
>
> Note, the logic here is very similar to 613f3255a35a, only difference
> is that leaving L0s enabled does not cause issues (at least
> I never encountered them myself when testing on the device) as its
> not dependent on CLKREQ# being physically there.
> Since there is already a way of specifying its presence in the DT,
> the driver should be aware and disable L1.
>
> Fixes: f3ac2ff14834 ("PCI/ASPM: Enable all ClockPM and ASPM states for devicetree platforms")
> Signed-off-by: Michal Gorlas <michal.gorlas@xxxxxxxxxxxxx>
> Tested-by: Richard Zhu <hongxing.zhu@xxxxxxx>
> Reviewed-by: Richard Zhu <hongxing.zhu@xxxxxxx>
> Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> ---
> Changes in v3:
> - pick up the reviewed-by tag
> - Link to v2: https://patch.msgid.link/20260827-l1-conditional-imx-v2-1-40b324aa2a94@xxxxxxxxxxxxx
>
> Changes in v2:
> - disable L1 unconditionally on resume for platforms advertising
> IMX_PCIE_FLAG_BROKEN_SUSPEND (Sashiko)
> - typos in the commit message
> - Link to v1: https://patch.msgid.link/20260719-l1-conditional-imx-v1-1-a55a57915c68@xxxxxxxxxxxxx
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 98e1db751132..1fdcbcd2422e 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -1318,6 +1318,22 @@ static void imx_pcie_assert_perst(struct imx_pcie *imx_pcie, bool assert)
>  	}
>  }
>  
> +static void imx_pcie_disable_l1(struct dw_pcie *pci)
> +{
> +	u32 val;
> +	u8 offset;
> +
> +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +
> +	dw_pcie_dbi_ro_wr_en(pci);
> +
> +	val = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
> +	val &= ~PCI_EXP_LNKCAP_ASPM_L1;
> +	dw_pcie_writel_dbi(pci, offset + PCI_EXP_LNKCAP, val);
> +
> +	dw_pcie_dbi_ro_wr_dis(pci);
> +}
> +
>  static int imx_pcie_host_init(struct dw_pcie_rp *pp)
>  {
>  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> @@ -1442,6 +1458,9 @@ static int imx_pcie_host_init(struct dw_pcie_rp *pp)
>  
>  	imx_setup_phy_mpll(imx_pcie);
>  
> +	if (!imx_pcie->supports_clkreq)
> +		imx_pcie_disable_l1(pci);
> +
>  	return 0;
>  
>  err_phy_off:
> @@ -1748,6 +1767,7 @@ static int imx_pcie_resume_noirq(struct device *dev)
>  			return ret;
>  		imx_pcie_deassert_core_reset(imx_pcie);
>  		imx_pcie_assert_perst(imx_pcie, false);
> +		imx_pcie_disable_l1(imx_pcie->pci);
>  
>  		/*
>  		 * Using PCIE_TEST_PD seems to disable MSI and powers down the
>
> ---
> base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
> change-id: 20260713-l1-conditional-imx-c2bfd20ae085
>
> Best regards,
> --  
> Michal Gorlas <michal.gorlas@xxxxxxxxxxxxx>
>
>