PCI: imx6: Do not wait for speed change on i.MX7

As can be seen from [1]:

  "...the different behavior between iMX6Q PCIe and iMX7D PCIe maybe caused
  by the different controller version.

  Regarding to the DOC description, the DIRECT_SPEED_CHANGE should be
  cleared after the speed change from GEN1 to GEN2. Unfortunately, when
  GEN1 device is used, the behavior is not documented.

  So, IC design guys run the simulation and find out the following
  behaviors:

     1. DIRECT_SPEED_CHANGE will be cleared in 7D after speed change
     	from GEN1 to GEN2. This matches doc’s description

     2. set MAX link speed(PCIE_CAP_TARGET_LINK_SPEED=0x01) as GEN1 and
     	re-run the simulation, DIRECT_SPEED_CHANGE will not be cleared;
     	remain as 1, this matches your result, but function test is
     	passed, so this bit should not affect the normal PCIe function."

imx6_pcie_wait_for_speed_change() will report false failures for Gen1 ->
Gen1 speed transition, so avoid doing that check and just rely on
imx6_pcie_wait_for_link() only.

[1] https://community.nxp.com/message/867943

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Cc: yurovsky@gmail.com
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Dong Aisheng <dongas86@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org

drivers/pci/dwc/pci-imx6.c

@@ -545,10 +545,21 @@ static int imx6_pcie_establish_link(struct imx6_pcie *imx6_pcie)
 	tmp |= PORT_LOGIC_SPEED_CHANGE;
 	dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, tmp);
 
-	ret = imx6_pcie_wait_for_speed_change(imx6_pcie);
-	if (ret) {
-		dev_err(dev, "Failed to bring link up!\n");
-		goto err_reset_phy;
+	if (imx6_pcie->variant != IMX7D) {
+		/*
+		 * On i.MX7, DIRECT_SPEED_CHANGE behaves differently
+		 * from i.MX6 family when no link speed transition
+		 * occurs and we go Gen1 -> yep, Gen1. The difference
+		 * is that, in such case, it will not be cleared by HW
+		 * which will cause the following code to report false
+		 * failure.
+		 */
+
+		ret = imx6_pcie_wait_for_speed_change(imx6_pcie);
+		if (ret) {
+			dev_err(dev, "Failed to bring link up!\n");
+			goto err_reset_phy;
+		}
 	}
 
 	/* Make sure link training is finished as well! */