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

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

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);
+
 	return 0;
 
 err_phy_off:

---
base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
change-id: 20260713-l1-conditional-imx-c2bfd20ae085

Best regards,
--  
Michal Gorlas <michal.gorlas@9elements.com>