[PATCH 2/2] arm: mvebu: theadorable: Set deephasis bit in PCIe configs very early

[Stefan Roese]

Testing has shown, that the quality of the PCIe signals and also the
stability of correct link establishment on the 2 PCIe ports is better,
when the deemphasis bit is set in the PCIe config register.

This needs to be done very early, even before the SERDES setup code is
run. This way, the first link will already be established with this
setup.

Signed-off-by: Stefan Roese <sr at denx.de>
---
 board/theadorable/theadorable.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/board/theadorable/theadorable.c b/board/theadorable/theadorable.c
index 4b99d9842efd..dd7f900773d6 100644
--- a/board/theadorable/theadorable.c
+++ b/board/theadorable/theadorable.c
@@ -148,6 +148,18 @@ u8 board_sat_r_get(u8 dev_num, u8 reg)
 	return 0xe;	/* PEX port 0 is PCIe Gen1, PEX port 1..3 PCIe Gen2 */
 }
 
+#define PCIE_LNK_CTRL_STAT_2_OFF	0x0090
+#define PCIE_LNK_CTRL_STAT_2_DEEM_BIT	BIT(6)
+
+static void pcie_set_deemphasis(u32 base)
+{
+	u32 reg;
+
+	reg = readl((void *)base + PCIE_LNK_CTRL_STAT_2_OFF);
+	reg |= PCIE_LNK_CTRL_STAT_2_DEEM_BIT;
+	writel(reg, (void *)base + PCIE_LNK_CTRL_STAT_2_OFF);
+}
+
 int board_early_init_f(void)
 {
 	/* Configure MPP */
@@ -169,6 +181,18 @@ int board_early_init_f(void)
 	writel(THEADORABLE_GPP_OUT_VAL_HIGH, MVEBU_GPIO2_BASE + 0x00);
 	writel(THEADORABLE_GPP_OUT_ENA_HIGH, MVEBU_GPIO2_BASE + 0x04);
 
+	/*
+	 * Set deephasis bit in the PCIe configuration of both PCIe ports
+	 * used on this board.
+	 *
+	 * This needs to be done very early, even before the SERDES setup
+	 * code is run. This way, the first link will already be established
+	 * with this setup. Testing has shown, that this results in a more
+	 * stable PCIe link with better signal quality.
+	 */
+	pcie_set_deemphasis(MVEBU_REG_PCIE_BASE);		/* Port 0 */
+	pcie_set_deemphasis(MVEBU_REG_PCIE_BASE + 0x2000);	/* Port 2 */
+
 	return 0;
 }
 
-- 
2.30.0