[PATCH] ARM64: juno: disable NOR flash node by default

[Linus Walleij]

After discussing on the mailing list it turns out that
accessing the flash memory from the kernel can disrupt CPU
sleep states and CPU hotplugging, so let's disable this
DT node by default. Setups that want to access the flash
can modify this entry to enable the flash again.

Quoting Sudeep Holla: "the firmware assumes the flash is
always in read mode while Linux leaves NOR flash in
"read id" mode after initialization."

Reported-by: Sudeep Holla <sudeep.holla at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Sudeep Holla <sudeep.holla at arm.com>
Cc: Liviu Dudau <Liviu.Dudau at arm.com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Leif Lindholm <leif.lindholm at arm.com>
Cc: Ryan Harkin <ryan.harkin at linaro.org>
Fixes: 5078f77e1443 "ARM64: juno: add NOR flash to device tree"
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
ARM SoC folks: please apply this as a fix for the upcoming v4.4
merge window, directly to the branch where the original commit
resides (appears to be directly on the for-next branch or
something).
---
 arch/arm64/boot/dts/arm/juno-motherboard.dtsi | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/boot/dts/arm/juno-motherboard.dtsi b/arch/arm64/boot/dts/arm/juno-motherboard.dtsi
index c7c99a42e2e9..8c029ee2a5b5 100644
--- a/arch/arm64/boot/dts/arm/juno-motherboard.dtsi
+++ b/arch/arm64/boot/dts/arm/juno-motherboard.dtsi
@@ -109,6 +109,13 @@
 				linux,part-probe = "afs";
 				reg = <0 0x00000000 0x04000000>;
 				bank-width = <4>;
+				/*
+				 * Unfortunately, accessing the flash disturbs
+				 * the CPU idle states (suspend) and CPU
+				 * hotplug of the platform. For this reason,
+				 * flash hardware access is disabled by default.
+				 */
+				status = "disabled";
 			};
 
 			ethernet at 2,00000000 {
-- 
2.4.3