imx6: kernel: backport an upstream pci hang fix

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42144 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/imx6/patches-3.14/0055-pci_imx6_fix-boot-hang-when-link-already-enabled.patch

+This fixes a boot hang observed when the bootloader
+already enabled the PCIe link for it's own use. The
+fundamental problem is that Freescale forgot to wire
+up the core reset, so software doesn't have a sane way
+to get the core into a defined state.
+
+According to the DW PCIe core reference manual configuration
+of the core may only happen when the LTSSM is disabled, so
+this is one of the first things we need to do. Apparently
+this isn't safe to do when the LTSSM is in any other state
+than "detect" as we observe an instant machine hang when
+trying to do so while the link is already up.
+
+As a workaround force LTSSM into detect state right before
+hitting the disable switch.
+
+Reported-by: Fabio Estevam <fabio.estevam <at> freescale.com>
+Signed-off-by: Lucas Stach <l.stach <at> pengutronix.de>
+Acked-by: Tim Harvey <tharvey <at> gateworks.com>
+--- a/drivers/pci/host/pci-imx6.c
++++ b/drivers/pci/host/pci-imx6.c
+@@ -52,6 +52,9 @@ struct imx6_pcie {
+ 
+ /* PCIe Port Logic registers (memory-mapped) */
+ #define PL_OFFSET 0x700
++#define PCIE_PL_PFLR (PL_OFFSET + 0x08)
++#define PCIE_PL_PFLR_LINK_STATE_MASK		(0x3f << 16)
++#define PCIE_PL_PFLR_FORCE_LINK			(1 << 15)
+ #define PCIE_PHY_DEBUG_R0 (PL_OFFSET + 0x28)
+ #define PCIE_PHY_DEBUG_R1 (PL_OFFSET + 0x2c)
+ #define PCIE_PHY_DEBUG_R1_XMLH_LINK_IN_TRAINING	(1 << 29)
+@@ -217,6 +220,31 @@ static int imx6q_pcie_abort_handler(unsi
+ static int imx6_pcie_assert_core_reset(struct pcie_port *pp)
+ {
+ 	struct imx6_pcie *imx6_pcie = to_imx6_pcie(pp);
++	u32 val, gpr1, gpr12;
++
++	/*
++	 * If the bootloader already enabled the link we need some special
++	 * handling to get the core back into a state where it is safe to
++	 * touch it for configuration. As there is no dedicated reset signal
++	 * wired up for MX6QDL, we need to manually force LTSSM into "detect"
++	 * state before completely disabling LTSSM, which is a prerequisite
++	 * for core configuration.
++	 * If both LTSSM_ENABLE and REF_SSP_ENABLE are active we have a strong
++	 * indication that the bootloader activated the link.
++	 */
++	regmap_read(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1, &gpr1);
++	regmap_read(imx6_pcie->iomuxc_gpr, IOMUXC_GPR12, &gpr12);
++
++	if ((gpr1 & IMX6Q_GPR1_PCIE_REF_CLK_EN) &&
++	    (gpr12 & IMX6Q_GPR12_PCIE_CTL_2)) {
++		val = readl(pp->dbi_base + PCIE_PL_PFLR);
++		val &= ~PCIE_PL_PFLR_LINK_STATE_MASK;
++		val |= PCIE_PL_PFLR_FORCE_LINK;
++		writel(val, pp->dbi_base + PCIE_PL_PFLR);
++
++		regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR12,
++				IMX6Q_GPR12_PCIE_CTL_2, 0 << 10);
++	}
+ 
+ 	regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
+ 			IMX6Q_GPR1_PCIE_TEST_PD, 1 << 18);
+@@ -627,6 +655,14 @@ static int __init imx6_pcie_probe(struct
+ 	return 0;
+ }
+ 
++static void imx6_pcie_shutdown(struct platform_device *pdev)
++{
++	struct imx6_pcie *imx6_pcie = platform_get_drvdata(pdev);
++
++	/* bring down link, so bootloader gets clean state in case of reboot */
++	imx6_pcie_assert_core_reset(&imx6_pcie->pp);
++}
++
+ static const struct of_device_id imx6_pcie_of_match[] = {
+ 	{ .compatible = "fsl,imx6q-pcie", },
+ 	{},
+@@ -639,6 +675,7 @@ static struct platform_driver imx6_pcie_
+ 		.owner	= THIS_MODULE,
+ 		.of_match_table = imx6_pcie_of_match,
+ 	},
++	.shutdown = imx6_pcie_shutdown,
+ };
+ 
+ /* Freescale PCIe driver does not allow module unload */