Patch "ARM: BCM5301X: Add back handler ignoring external imprecise aborts" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ARM: BCM5301X: Add back handler ignoring external imprecise aborts

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm-bcm5301x-add-back-handler-ignoring-external-imprecise-aborts.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <[email protected]>
Date: Sat, 29 Oct 2016 13:12:29 +0200
Subject: ARM: BCM5301X: Add back handler ignoring external imprecise aborts
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From: Rafał Miłecki <[email protected]>

commit 09f3510fb70a46c8921f2cf4a90dbcae460a6820 upstream.

Since early BCM5301X days we got abort handler that was removed by commit 937b12306ea79 ("ARM: BCM5301X: remove workaround imprecise abort fault handler"). It assumed we need to deal only with pending aborts left by the bootloader. Unfortunately this isn't true for BCM5301X.

When probing PCI config space (device enumeration) it is expected to have master aborts on the PCI bus. Most bridges don't forward (or they allow disabling it) these errors onto the AXI/AMBA bus but not the Northstar (BCM5301X) one.

iProc PCIe controller on Northstar seems to be some older one, without a control register for errors forwarding. It means we need to workaround this at platform level. All newer platforms are not affected by this issue.

---
 arch/arm/mach-bcm/bcm_5301x.c |   28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

@@ -9,14 +9,42 @@
 #include <asm/hardware/cache-l2x0.h>
 
 #include <asm/mach/arch.h>
+#include <asm/siginfo.h>
+#include <asm/signal.h>
+
+#define FSR_EXTERNAL		(1 << 12)
+#define FSR_READ		(0 << 10)
+#define FSR_IMPRECISE		0x0406
 
 static const char *const bcm5301x_dt_compat[] __initconst = {
 	"brcm,bcm4708",
 	NULL,
 };
 
+static int bcm5301x_abort_handler(unsigned long addr, unsigned int fsr,
+				  struct pt_regs *regs)
+{
+	/*
+	 * We want to ignore aborts forwarded from the PCIe bus that are
+	 * expected and shouldn't really be passed by the PCIe controller.
+	 * The biggest disadvantage is the same FSR code may be reported when
+	 * reading non-existing APB register and we shouldn't ignore that.
+	 */
+	if (fsr == (FSR_EXTERNAL | FSR_READ | FSR_IMPRECISE))
+		return 0;
+
+	return 1;
+}
+
+static void __init bcm5301x_init_early(void)
+{
+	hook_fault_code(16 + 6, bcm5301x_abort_handler, SIGBUS, BUS_OBJERR,
+			"imprecise external abort");
+}
+
 DT_MACHINE_START(BCM5301X, "BCM5301X")
 	.l2c_aux_val	= 0,
 	.l2c_aux_mask	= ~0,
 	.dt_compat	= bcm5301x_dt_compat,
+	.init_early	= bcm5301x_init_early,
 MACHINE_END

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/arm-bcm5301x-add-back-handler-ignoring-external-imprecise-aborts.patch