[PATCH 1/2] PCI: mediatek-gen3: Fix PERST# control timing during system startup

[Jian Yang]

Some of MediaTek's chip will stop generating REFCLK if the
PCIE_PHY_RSTB signal of PCIe controller is asserted.

We have to adjust the control timing as follows to ensure that PERST#
will be de-asserted after the REFCLK is stable:
Assert all reset signals -> delay 10ms -> De-assert all reset signals
except PERST# -> delay 100ms -> De-assert PERST#

Signed-off-by: Jian Yang <jian.yang@xxxxxxxxxxxx>
---
 drivers/pci/controller/pcie-mediatek-gen3.c | 25 ++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
index b0accd828589..58ba1aa35a22 100644
--- a/drivers/pci/controller/pcie-mediatek-gen3.c
+++ b/drivers/pci/controller/pcie-mediatek-gen3.c
@@ -62,6 +62,11 @@
 #define PCIE_PHY_RSTB			BIT(1)
 #define PCIE_BRG_RSTB			BIT(2)
 #define PCIE_PE_RSTB			BIT(3)
+/*
+ * Described in the datasheet of MediaTek PCIe Gen3 controller.
+ * After set PCIE_BRG_RSTB, wait 10ms before accessing PCIe internal registers.
+ */
+#define PCIE_BRG_RST_RDY_MS		10
 
 #define PCIE_LTSSM_STATUS_REG		0x150
 #define PCIE_LTSSM_STATE_MASK		GENMASK(28, 24)
@@ -430,6 +435,21 @@ static int mtk_pcie_devices_power_up(struct mtk_gen3_pcie *pcie)
 		return err;
 	}
 
+	/*
+	 * Some of MediaTek's chips won't output REFCLK when PCIE_PHY_RSTB is
+	 * asserted, we have to de-assert MAC & PHY & BRG reset signals first
+	 * to allow the REFCLK to be stable. While PCIE_BRG_RSTB is asserted,
+	 * there is a short period during which the PCIe internal register
+	 * cannot be accessed, so we need to wait 10ms here.
+	 */
+	msleep(PCIE_BRG_RST_RDY_MS);
+
+	if (!(pcie->soc->flags & SKIP_PCIE_RSTB)) {
+		/* De-assert MAC, PHY and BRG reset signals */
+		val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB);
+		writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
+	}
+
 	/*
 	 * Described in PCIe CEM specification revision 6.0.
 	 *
@@ -439,9 +459,8 @@ static int mtk_pcie_devices_power_up(struct mtk_gen3_pcie *pcie)
 	msleep(PCIE_T_PVPERL_MS);
 
 	if (!(pcie->soc->flags & SKIP_PCIE_RSTB)) {
-		/* De-assert reset signals */
-		val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB |
-			 PCIE_PE_RSTB);
+		/* De-assert PERST# signal */
+		val &= ~PCIE_PE_RSTB;
 		writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
 	}
 
-- 
2.45.2