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

["Michal Gorlas" <michal.gorlas@9elements.com>]

On Wed Jul 29, 2026 at 7:01 PM CEST, Manivannan Sadhasivam wrote:
> On Sun, Jul 19, 2026 at 02:47:54AM +0200, 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 iMX SoCs
>> (for e.g. iMX 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.
>> 
>> Hence, disable L1 capability in the LINKCAP register if supports-clkreq
>> is not set in the DT explicitly.
>> 
>> 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@9elements.com>
>> ---
>>  drivers/pci/controller/dwc/pci-imx6.c | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>> 
>> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
>> index 98e1db751132..7471501fbf04 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);
>
> Sashiko raised a valid issue here:
> https://patchwork.kernel.org/project/linux-pci/patch/20260719-l1-conditional-imx-v1-1-a55a57915c68@9elements.com/#27076171
>
> IMX_PCIE_FLAG_BROKEN_SUSPEND is only set for i.MX6Q, but none of its DTs have
> 'supports-clkreq' property. So this patch will impact them also and since they
> do not reinitialize the hardware fully in resume(), ASPM settings will reset to
> hardware default.

Right, for i.MX6Q, imx_pcie_disable_l1() could be called unconditionally
in imx_pcie_resume_noirq() after the imx_check_flag(imx_pcie, IMX_PCIE_FLAG_BROKEN_SUSPEND)
block, something like:

@@ -1767,6 +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

Though I do not have imx6q hw to test this, so it would be nice if NXP
folks could give it a test.

Best,
Michal