linux-kernel - [PATCH v1 1/3] ARM: tegra: Initialize r0 register for firmware wake-up

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Date:   Wed, 25 Mar 2020 01:43:33 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Jasper Korten <jja2000@...il.com>,
        David Heidelberg <david@...t.cz>,
        Peter Geis <pgwipeout@...il.com>
Cc:     linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/3] ARM: tegra: Initialize r0 register for firmware wake-up

Downstream kernel of ASUS TF300T sets r0 to #3. There is no explanation in
downstream code whether this is really needed and some of T30 downstream
kernels have and explicit comment telling that all arguments are ignored
by firmware. Let's take a safe side by replicating behavior of the TF300T
downstream kernel. This change works fine on Ouya and Nexus 7 devices.

Tested-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
Tested-by: Jasper Korten <jja2000@...il.com>
Tested-by: David Heidelberg <david@...t.cz>
Tested-by: Peter Geis <pgwipeout@...il.com>
Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 arch/arm/mach-tegra/reset-handler.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-tegra/reset-handler.S b/arch/arm/mach-tegra/reset-handler.S
index 53123ae4ac3b..06ca44b09381 100644
--- a/arch/arm/mach-tegra/reset-handler.S
+++ b/arch/arm/mach-tegra/reset-handler.S
@@ -98,7 +98,12 @@ ENTRY(tegra_resume_trusted_foundations)
 	reteq	lr
 
  .arch_extension sec
-	/* First call after suspend wakes firmware. No arguments required. */
+	/*
+	 * First call after suspend wakes firmware. No arguments required
+	 * for some firmware versions. Downstream kernel of ASUS TF300T uses
+	 * r0=3 for the wake-up notification.
+	 */
+	mov	r0, #3
 	smc	#0
 
 	b	cpu_resume
-- 
2.25.1