[PATCH] PCI: imx6: fix downstream bus scanning

[Lucas Stach]

The change in Linux 4.12 to make PCI configuartion requests non-posted
means that we are now getting a synchronous abort when the CFG space
read to probe for downstream devices times out.

Synchronous aborts need to be handled differently from the async aborts
we were getting before, in particular the PC needs to be advanced when
resolving the abort. This is mostly a copy of what other PCI drivers do
on ARM to handle those aborts.

Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
This is a fix that needs to go in for 4.12, but I would hope to get
some thorough testing before.
---
 drivers/pci/dwc/pci-imx6.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/dwc/pci-imx6.c b/drivers/pci/dwc/pci-imx6.c
index a98cba55c7f0..19a289b8cc94 100644
--- a/drivers/pci/dwc/pci-imx6.c
+++ b/drivers/pci/dwc/pci-imx6.c
@@ -252,7 +252,34 @@ static void imx6_pcie_reset_phy(struct imx6_pcie *imx6_pcie)
 static int imx6q_pcie_abort_handler(unsigned long addr,
 		unsigned int fsr, struct pt_regs *regs)
 {
-	return 0;
+	unsigned long pc = instruction_pointer(regs);
+	unsigned long instr = *(unsigned long *)pc;
+	int reg = (instr >> 12) & 15;
+
+	/*
+	 * If the instruction being executed was a read,
+	 * make it look like it read all-ones.
+	 */
+	if ((instr & 0x0c100000) == 0x04100000) {
+		unsigned long val;
+
+		if (instr & 0x00400000)
+			val = 255;
+		else
+			val = -1;
+
+		regs->uregs[reg] = val;
+		regs->ARM_pc += 4;
+		return 0;
+	}
+
+	if ((instr & 0x0e100090) == 0x00100090) {
+		regs->uregs[reg] = -1;
+		regs->ARM_pc += 4;
+		return 0;
+	}
+
+	return 1;
 }
 
 static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
@@ -819,8 +846,8 @@ static int __init imx6_pcie_init(void)
 	 * we can install the handler here without risking it
 	 * accessing some uninitialized driver state.
 	 */
-	hook_fault_code(16 + 6, imx6q_pcie_abort_handler, SIGBUS, 0,
-			"imprecise external abort");
+	hook_fault_code(8, imx6q_pcie_abort_handler, SIGBUS, 0,
+			"external abort on non-linefetch");
 
 	return platform_driver_register(&imx6_pcie_driver);
 }
-- 
2.11.0