[PATCH soc/next] ARM: BCM53573: Add custom init_time with arch timer workaroud

[Rafał Miłecki]

From: Rafał Miłecki <rafal at milecki.pl>

BCM53573 uses ARM architected timer but CFE (bootloader) is bugged and
doesn't setup hardware properly. As the architecture requirement clock
should be enabled and CNTFRQ should be set before starting Linux.

Unfortunately it's impossible to have CFE fixed and updated on all
released devices. There are plenty of them on the market and updating
bootloader isn't a standard procedure. We also don't have CFE sources
for BCM53573 devices and no replacement bootloader.

We can't modify arch timer to simply accept specifying clock. Quoting
Mark: "The clock-frequency property is at best a dodgy workaround, and
this is even worse.". Marc also noted that other subsystems may rely on
CNTFRQ as well.

The only sane workaround seems to be fixing this CFE bug in BCM53573
arch code. It doesn't require modifying other drivers and should allow
all subsystems to work correctly.

Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Marc Zyngier <marc.zyngier at arm.com>
---
 MAINTAINERS                   |  1 +
 arch/arm/mach-bcm/Makefile    |  3 +++
 arch/arm/mach-bcm/bcm_53573.c | 62 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)
 create mode 100644 arch/arm/mach-bcm/bcm_53573.c

diff --git a/MAINTAINERS b/MAINTAINERS
index a91bca7..0bb0c4b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2568,6 +2568,7 @@ BROADCOM BCM53573 ARM ARCHITECTURE
 M:	Rafał Miłecki <rafal at milecki.pl>
 L:	linux-arm-kernel at lists.infradead.org
 S:	Maintained
+F:	arch/arm/mach-bcm/bcm_53573.c
 F:	arch/arm/boot/dts/bcm53573*
 F:	arch/arm/boot/dts/bcm47189*
 
diff --git a/arch/arm/mach-bcm/Makefile b/arch/arm/mach-bcm/Makefile
index 980f585..0d64778 100644
--- a/arch/arm/mach-bcm/Makefile
+++ b/arch/arm/mach-bcm/Makefile
@@ -50,6 +50,9 @@ ifeq ($(CONFIG_ARCH_BCM_5301X),y)
 obj-$(CONFIG_SMP)		+= platsmp.o
 endif
 
+# BCM53573
+obj-$(CONFIG_ARCH_BCM_53573)	+= bcm_53573.o
+
 # BCM63XXx
 ifeq ($(CONFIG_ARCH_BCM_63XX),y)
 obj-y				+= bcm63xx.o
diff --git a/arch/arm/mach-bcm/bcm_53573.c b/arch/arm/mach-bcm/bcm_53573.c
new file mode 100644
index 0000000..540a247
--- /dev/null
+++ b/arch/arm/mach-bcm/bcm_53573.c
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2016 Rafał Miłecki <rafal at milecki.pl>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <asm/mach/arch.h>
+#include <linux/clk-provider.h>
+#include <linux/clocksource.h>
+#include <linux/clk.h>
+
+static inline void arch_timer_set_cntfrq(u32 cntfrq)
+{
+	asm volatile("mcr p15, 0, %0, c14, c0, 0" : : "r" (cntfrq));
+}
+
+/*
+ * CFE bootloader doesn't meet arch requirements. It doesn't enable ILP clock
+ * which is required for arch timer and doesn't set CNTFRQ.
+ * Fix is up here.
+ */
+static void __init bcm_53573_setup_arch_timer(void)
+{
+	struct of_phandle_args out_args = { };
+	struct clk *clk;
+
+	out_args.np = of_find_compatible_node(NULL, NULL, "brcm,bcm53573-ilp");
+	if (!out_args.np) {
+		pr_warn("Failed to find ILP node\n");
+		return;
+	}
+
+	clk = of_clk_get_from_provider(&out_args);
+	if (!IS_ERR(clk)) {
+		if (!clk_prepare_enable(clk))
+			arch_timer_set_cntfrq(clk_get_rate(clk));
+	}
+
+	of_node_put(out_args.np);
+}
+
+/* A copy of ARM's time_init with workaround inserted */
+static void __init bcm_53573_init_time(void)
+{
+#ifdef CONFIG_COMMON_CLK
+	of_clk_init(NULL);
+#endif
+	bcm_53573_setup_arch_timer();
+	clocksource_probe();
+}
+
+static const char *const bcm_53573_dt_compat[] __initconst = {
+	"brcm,bcm53573",
+	NULL,
+};
+
+DT_MACHINE_START(BCM5301X, "BCM53573")
+	.init_time	= bcm_53573_init_time,
+	.dt_compat	= bcm_53573_dt_compat,
+MACHINE_END
-- 
2.9.3