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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Yifeng Li <tomli@tomli.me>,
        Paul Burton <paul.burton@mips.com>, linux-mips@vger.kernel.org,
        Huacai Chen <chenhc@lemote.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        James Hogan <jhogan@kernel.org>,
        Aaro Koskinen <aaro.koskinen@iki.fi>
Subject: [PATCH 4.20 27/50] mips: loongson64: remove unreachable(), fix loongson_poweroff().
Date:   Wed, 13 Feb 2019 19:38:32 +0100
Message-Id: <20190213183657.921615249@linuxfoundation.org>
In-Reply-To: <20190213183655.747168774@linuxfoundation.org>
References: <20190213183655.747168774@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yifeng Li <tomli@tomli.me>

commit 8a96669d77897ff3613157bf43f875739205d66d upstream.

On my Yeeloong 8089, I noticed the machine fails to shutdown
properly, and often, the function mach_prepare_reboot() is
unexpectedly executed, thus the machine reboots instead. A
wait loop is needed to ensure the system is in a well-defined
state before going down.

In commit 997e93d4df16 ("MIPS: Hang more efficiently on
halt/powerdown/restart"), a general superset of the wait loop for all
platforms is already provided, so we don't need to implement our own.

This commit simply removes the unreachable() compiler marco after
mach_prepare_reboot(), thus allowing the execution of machine_hang().
My test shows that the machine is now able to shutdown successfully.

Please note that there are two different bugs preventing the machine
from shutting down, another work-in-progress commit is needed to
fix a lockup in cpufreq / i8259 driver, please read Reference, this
commit does not fix that bug.

Reference: https://lkml.org/lkml/2019/2/5/908
Signed-off-by: Yifeng Li <tomli@tomli.me>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: stable@vger.kernel.org # v4.17+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/loongson64/common/reset.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/mips/loongson64/common/reset.c
+++ b/arch/mips/loongson64/common/reset.c
@@ -59,7 +59,12 @@ static void loongson_poweroff(void)
 {
 #ifndef CONFIG_LEFI_FIRMWARE_INTERFACE
 	mach_prepare_shutdown();
-	unreachable();
+
+	/*
+	 * It needs a wait loop here, but mips/kernel/reset.c already calls
+	 * a generic delay loop, machine_hang(), so simply return.
+	 */
+	return;
 #else
 	void (*fw_poweroff)(void) = (void *)loongson_sysconf.poweroff_addr;