linux-kernel - [PATCH] ARM: mach-shmobile: Don't configure ARCH timer if PSCI is enabled

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Date:   Wed, 17 Apr 2019 20:10:40 +0300
From:   Oleksandr Tyshchenko <olekstysh@...il.com>
To:     linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     julien.grall@....com, horms@...ge.net.au, magnus.damm@...il.com,
        linux@...linux.org.uk,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: [PATCH] ARM: mach-shmobile: Don't configure ARCH timer if PSCI is enabled

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

If CONFIG_PSCI is enabled then most likely we are running on
PSCI-enabled U-Boot which, we assume, has already taken care of
configuring ARCH timer stuff before switching to non-secure mode.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

---
A bit of context here...

We are highly interested in Renesas "Stout" board support (r8a7790)
in Xen hypervisor. The reason is to have fully supported HW for
performing "OSSTEST" (Xen automatic test system) on ARM32.

To reach that target we need a "generic way" for the secondary CPU cores
bring up and switching them to non-secure hyp mode.
So, the PSCI as a generic well-known way to bring up CPUs, was chosen
for that purpose. 

You can find corresponding patches for U-Boot here:
http://u-boot.10912.n7.nabble.com/PATCH-0-3-PSCI-support-for-r8a7790-SoC-Lager-Stout-boards-td357352.html

You can find corresponding patches for Xen hypervisor here:
https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg43332.html

To sumarize:
Together with enabling CONFIG_PSCI in shmobile_defconfig, current patch
is a minimal required change needed to run mainline Linux on top of
PSCI-enabled U-Boot.
There is no need to modify device tree. U-Boot will take care of inserting
proper "enable-method" strings in CPU nodes.

---
 arch/arm/mach-shmobile/setup-rcar-gen2.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-shmobile/setup-rcar-gen2.c b/arch/arm/mach-shmobile/setup-rcar-gen2.c
index eea60b2..bac4490 100644
--- a/arch/arm/mach-shmobile/setup-rcar-gen2.c
+++ b/arch/arm/mach-shmobile/setup-rcar-gen2.c
@@ -32,7 +32,7 @@ static const struct of_device_id cpg_matches[] __initconst = {
 	{ /* sentinel */ }
 };

-static unsigned int __init get_extal_freq(void)
+static unsigned int __init __maybe_unused get_extal_freq(void)
 {
 	const struct of_device_id *match;
 	struct device_node *cpg, *extal;
@@ -60,6 +60,12 @@ static unsigned int __init get_extal_freq(void)

 void __init rcar_gen2_timer_init(void)
 {
+/*
+ * If CONFIG_PSCI is enabled then most likely we are running on PSCI-enabled
+ * U-Boot which, we assume, has already taken care of configuring ARCH timer
+ * stuff before switching to non-secure mode.
+ */
+#if !defined(CONFIG_ARM_PSCI)
 	void __iomem *base;
 	u32 freq;

@@ -101,6 +107,7 @@ void __init rcar_gen2_timer_init(void)
 	}

 	iounmap(base);
+#endif /* #if !defined(CONFIG_ARM_PSCI) */

 	of_clk_init(NULL);
 	timer_probe();
-- 
2.7.4