PCI: imx6: Wait for clocks to stabilize after ref_en

Richard Zhu · bjorn-helgaas · commit a2fa6f64c26a · 2014-10-29T10:11:54.000-06:00
For boards without a reset GPIO we skip the delay between enabling the pcie_ref_clk and touching the RC registers for configuration. This hangs the system if there isn't a proper delay to ensure the clocks are settled in the DW PCIe core. Also iMX6Q always needs an additional 10us delay to make sure the reset is propagated through the core, as we don't have an explicitly controlled reset input on this SoC. This fixes a problem with 3fce0e8 ("PCI: imx6: Delay enabling reference clock for SS until it stabilizes"): the kernel doesn't boot on systems that don't pass the PCI GPIO reset in the DTB. This regression affects mx6 nitrogen boards. [bhelgaas: add regression info in changelog] Fixes: 3fce0e8 ("PCI: imx6: Delay enabling reference clock for SS until it stabilizes") Reported-by: Fabio Estevam <fabio.estevam@freescale.com> Tested-by: Fabio Estevam <fabio.estevam@freescale.com> Signed-off-by: Richard Zhu <richard.zhu@freescale.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Lucas Stach <l.stach@pengutronix.de>
diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
@@ -275,15 +275,22 @@ static int imx6_pcie_deassert_core_reset(struct pcie_port *pp)
 		goto err_pcie;
 	}
 
-	/* allow the clocks to stabilize */
-	usleep_range(200, 500);
-
 	/* power up core phy and enable ref clock */
 	regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
 			IMX6Q_GPR1_PCIE_TEST_PD, 0 << 18);
+	/*
+	 * the async reset input need ref clock to sync internally,
+	 * when the ref clock comes after reset, internal synced
+	 * reset time is too short, cannot meet the requirement.
+	 * add one ~10us delay here.
+	 */
+	udelay(10);
 	regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
 			IMX6Q_GPR1_PCIE_REF_CLK_EN, 1 << 16);
 
+	/* allow the clocks to stabilize */
+	usleep_range(200, 500);
+
 	/* Some boards don't have PCIe reset GPIO. */
 	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
 		gpio_set_value(imx6_pcie->reset_gpio, 0);
