linux-kernel - [PATCH 3/3] powerpc: dts: turris1x.dts: Set lower priority for CPLD syscon-reboot

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Date:   Sat, 20 Aug 2022 12:29:25 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Marek Behún <kabel@...nel.org>
Subject: [PATCH 3/3] powerpc: dts: turris1x.dts: Set lower priority for CPLD syscon-reboot

Due to CPLD firmware bugs, set CPLD syscon-reboot priority level to 64
(between rstcr and watchdog) to ensure that rstcr's global-utilities reset
method which is preferred stay as default one, and to ensure that CPLD
syscon-reboot is more preferred than watchdog reset method.

Fixes: 0531a4abd1c6 ("powerpc: dts: turris1x.dts: Add CPLD reboot node")
Signed-off-by: Pali Rohár <pali@...nel.org>
---
 arch/powerpc/boot/dts/turris1x.dts | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/powerpc/boot/dts/turris1x.dts b/arch/powerpc/boot/dts/turris1x.dts
index 69c38ed8a3a5..c189293d5a1e 100644
--- a/arch/powerpc/boot/dts/turris1x.dts
+++ b/arch/powerpc/boot/dts/turris1x.dts
@@ -353,11 +353,34 @@
 			};
 
 			reboot@d {
+				/*
+				 * CPLD firmware which manages system reset and
+				 * watchdog registers has bugs. It does not
+				 * autoclear system reset register after change
+				 * and watchdog ignores reset line on immediate
+				 * succeeding reset cycle triggered by watchdog.
+				 * These bugs have to be workarounded in U-Boot
+				 * bootloader. So use system reset via syscon as
+				 * a last resort because older U-Boot versions
+				 * do not have workaround for watchdog.
+				 *
+				 * Reset method via rstcr's global-utilities
+				 * (the preferred one) has priority level 128,
+				 * watchdog has priority level 0 and default
+				 * syscon-reboot priority level is 192.
+				 *
+				 * So define syscon-reboot with custom priority
+				 * level 64 (between rstcr and watchdog) because
+				 * rstcr should stay as default preferred reset
+				 * method and reset via watchdog is more broken
+				 * than system reset via syscon.
+				 */
 				compatible = "syscon-reboot";
 				reg = <0x0d 0x01>;
 				offset = <0x0d>;
 				mask = <0x01>;
 				value = <0x01>;
+				priority = <64>;
 			};
 
 			led-controller@13 {
-- 
2.20.1