drivers: pci: imx: fix imx_pcie_remove function

We have at least a minor count of boards, that failed to re-initialize
PCI express in the Linux kernel. Typical failure rate is 20% on affected
boards. This is mitigated by commit 6ecbe13756 ("drivers: pci: imx:
add imx_pcie_remove function").

However, at least on some i.MX6 custom boards, when calling
assert_core_reset() as part of the first-time PCIe init, read access
to PCIE_PL_PFLR simply hangs. Surround this readl() with
imx_pcie_fix_dabt_handler() does not help. For this reason, the forced
LTSSM detection is only used on the second assert_core_reset() that is
called shorly before starting the Linux kernel.

Signed-off-by: Sven-Ola Tuecke <sven-ola.tuecke@numberfour.eu>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: David Müller <d.mueller@elsoft.ch>

drivers/pci/pcie_imx.c

@@ -431,7 +431,7 @@ static int imx_pcie_write_config(struct pci_controller *hose, pci_dev_t d,
 /*
  * Initial bus setup
  */
-static int imx6_pcie_assert_core_reset(void)
+static int imx6_pcie_assert_core_reset(bool prepare_for_boot)
 {
 	struct iomuxc *iomuxc_regs = (struct iomuxc *)IOMUXC_BASE_ADDR;
 
@@ -459,7 +459,7 @@ static int imx6_pcie_assert_core_reset(void)
 	 * If both LTSSM_ENABLE and REF_SSP_ENABLE are active we have a strong
 	 * indication that the bootloader activated the link.
 	 */
-	if (is_mx6dq()) {
+	if (is_mx6dq() && prepare_for_boot) {
 		u32 val, gpr1, gpr12;
 
 		gpr1 = readl(&iomuxc_regs->gpr[1]);
@@ -605,7 +605,7 @@ static int imx_pcie_link_up(void)
 	uint32_t tmp;
 	int count = 0;
 
-	imx6_pcie_assert_core_reset();
+	imx6_pcie_assert_core_reset(false);
 	imx6_pcie_init_phy();
 	imx6_pcie_deassert_core_reset();
 
@@ -687,7 +687,7 @@ void imx_pcie_init(void)
 
 void imx_pcie_remove(void)
 {
-	imx6_pcie_assert_core_reset();
+	imx6_pcie_assert_core_reset(true);
 }
 
 /* Probe function. */