[PATCH v3] PCI: dw-rockchip: Prevent advertising L1 Substates support

[Niklas Cassel <cassel@kernel.org>]

The L1 substates support requires additional steps to work, namely:
-Proper handling of the CLKREQ# sideband signal. (It is mostly handled by
 hardware, but software still needs to set the clkreq fields in the
 PCIE_CLIENT_POWER_CON register to match the hardware implementation.)
-Program the frequency of the aux clock into the
 DSP_PCIE_PL_AUX_CLK_FREQ_OFF register. (During L1 substates the core_clk
 is turned off and the aux_clk is used instead.)

These steps are currently missing from the driver.

For more details, see section '18.6.6.4 L1 Substate' in the RK3658 TRM 1.1
Part 2, or section '11.6.6.4 L1 Substate' in the RK3588 TRM 1.0 Part2.

While this has always been a problem when using e.g.
CONFIG_PCIEASPM_POWER_SUPERSAVE=y, or when modifying
/sys/bus/pci/devices/.../link/l1_2_aspm, the lacking driver support for L1
substates became more apparent after commit f3ac2ff14834 ("PCI/ASPM:
Enable all ClockPM and ASPM states for devicetree platforms"), which
enabled ASPM also for CONFIG_PCIEASPM_DEFAULT=y.

When using e.g. an NVMe drive connected to the PCIe controller, the
problem will be seen as:
nvme nvme0: controller is down; will reset: CSTS=0xffffffff, PCI_STATUS=0x10
nvme nvme0: Does your device have a faulty power saving mode enabled?
nvme nvme0: Try "nvme_core.default_ps_max_latency_us=0 pcie_aspm=off pcie_port_pm=off" and report a bug

Thus, prevent advertising L1 Substates support until proper driver support
is added.

Cc: stable@vger.kernel.org
Fixes: 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
Fixes: f3ac2ff14834 ("PCI/ASPM: Enable all ClockPM and ASPM states for devicetree platforms")
Acked-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Changes since v2:
-Improve commit message (Bjorn)

 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index 3e2752c7dd09..84f882abbca5 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -200,6 +200,25 @@ static bool rockchip_pcie_link_up(struct dw_pcie *pci)
 	return FIELD_GET(PCIE_LINKUP_MASK, val) == PCIE_LINKUP;
 }
 
+/*
+ * See e.g. section '11.6.6.4 L1 Substate' in the RK3588 TRM V1.0 for the steps
+ * needed to support L1 substates. Currently, not a single rockchip platform
+ * performs these steps, so disable L1 substates until there is proper support.
+ */
+static void rockchip_pcie_disable_l1sub(struct dw_pcie *pci)
+{
+	u32 cap, l1subcap;
+
+	cap = dw_pcie_find_ext_capability(pci, PCI_EXT_CAP_ID_L1SS);
+	if (cap) {
+		l1subcap = dw_pcie_readl_dbi(pci, cap + PCI_L1SS_CAP);
+		l1subcap &= ~(PCI_L1SS_CAP_L1_PM_SS | PCI_L1SS_CAP_ASPM_L1_1 |
+			      PCI_L1SS_CAP_ASPM_L1_2 | PCI_L1SS_CAP_PCIPM_L1_1 |
+			      PCI_L1SS_CAP_PCIPM_L1_2);
+		dw_pcie_writel_dbi(pci, cap + PCI_L1SS_CAP, l1subcap);
+	}
+}
+
 static void rockchip_pcie_enable_l0s(struct dw_pcie *pci)
 {
 	u32 cap, lnkcap;
@@ -264,6 +283,7 @@ static int rockchip_pcie_host_init(struct dw_pcie_rp *pp)
 	irq_set_chained_handler_and_data(irq, rockchip_pcie_intx_handler,
 					 rockchip);
 
+	rockchip_pcie_disable_l1sub(pci);
 	rockchip_pcie_enable_l0s(pci);
 
 	return 0;
@@ -301,6 +321,7 @@ static void rockchip_pcie_ep_init(struct dw_pcie_ep *ep)
 	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
 	enum pci_barno bar;
 
+	rockchip_pcie_disable_l1sub(pci);
 	rockchip_pcie_enable_l0s(pci);
 	rockchip_pcie_ep_hide_broken_ats_cap_rk3588(ep);
 
-- 
2.51.0