ARM: OMAP: clocks: Delay clk inits atleast until slab is initialized

clk inits on OMAP happen quite early, even before slab is available.
The dependency comes from the fact that the timer init code starts to
use clocks and hwmod and we need clocks to be initialized by then.

There are various problems doing clk inits this early, one is,
not being able to do dynamic clk registrations and hence the
dependency on clk-private.h. The other is, inability to debug
early kernel crashes without enabling DEBUG_LL and earlyprintk.

Doing early clk init also exposed another instance of a kernel
panic due to a BUG() when CONFIG_DEBUG_SLAB is enabled.

[    0.000000] Kernel BUG at c01174f8 [verbose debug info unavailable]
[    0.000000] Internal error: Oops - BUG: 0 [#1] SMP ARM
[    0.000000] Modules linked in:
[    0.000000] CPU: 0    Not tainted  (3.9.0-rc1-12179-g72d48f9 #6)
[    0.000000] PC is at __kmalloc+0x1d4/0x248
[    0.000000] LR is at __clk_init+0x2e0/0x364
[    0.000000] pc : [<c01174f8>]    lr : [<c0441f54>]    psr: 600001d3
[    0.000000] sp : c076ff28  ip : c065cefc  fp : c0441f54
[    0.000000] r10: 0000001c  r9 : 000080d0  r8 : c076ffd4
[    0.000000] r7 : c074b578  r6 : c0794d88  r5 : 00000040  r4 : 00000000
[    0.000000] r3 : 00000000  r2 : c07cac70  r1 : 000080d0  r0 : 0000001c
[    0.000000] Flags: nZCv  IRQs off  FIQs off  Mode SVC_32  ISA ARM  Segment kernel
[    0.000000] Control: 10c53c7d  Table: 8000404a  DAC: 00000017
[    0.000000] Process swapper (pid: 0, stack limit = 0xc076e240)
[    0.000000] Stack: (0xc076ff28 to 0xc0770000)
[    0.000000] ff20:                   22222222 c0794ec8 c06546e8 00000000 00000040 c0794d88
[    0.000000] ff40: c074b578 c076ffd4 c07951c8 c076e000 00000000 c0441f54 c074b578 c076ffd4
[    0.000000] ff60: c0793828 00000040 c0794d88 c074b578 c076ffd4 c0776900 c076e000 c07272ac
[    0.000000] ff80: 2f800000 c074c968 c07f93d0 c0719780 c076ffa0 c076ff98 00000000 00000000
[    0.000000] ffa0: 00000000 00000000 00000000 00000001 c074cd6c c077b1ec 8000406a c0715724
[    0.000000] ffc0: 00000000 00000000 00000000 00000000 00000000 c074c968 10c53c7d c0776974
[    0.000000] ffe0: c074cd6c c077b1ec 8000406a 411fc092 00000000 80008074 00000000 00000000
[    0.000000] [<c01174f8>] (__kmalloc+0x1d4/0x248) from [<c0441f54>] (__clk_init+0x2e0/0x364)
[    0.000000] [<c0441f54>] (__clk_init+0x2e0/0x364) from [<c07272ac>] (omap4xxx_clk_init+0xbc/0x140)
[    0.000000] [<c07272ac>] (omap4xxx_clk_init+0xbc/0x140) from [<c0719780>] (setup_arch+0x15c/0x284)
[    0.000000] [<c0719780>] (setup_arch+0x15c/0x284) from [<c0715724>] (start_kernel+0x7c/0x334)
[    0.000000] [<c0715724>] (start_kernel+0x7c/0x334) from [<80008074>] (0x80008074)
[    0.000000] Code: e5883004 e1a00006 e28dd00c e8bd8ff0 (e7f001f2)
[    0.000000] ---[ end trace 1b75b31a2719ed1c ]---
[    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!

It was a know issue, that slab allocations would fail when common
clock core tries to cache parent pointers for mux clocks on OMAP,
and hence a patch 'clk: Allow late cache allocation for clk->parents,
commit 7975059d' was added to work this problem around.
A BUG() within kmalloc() with CONFIG_DEBUG_SLAB enabled was completely
overlooked causing this regression.

More details on the issue reported can be found here,
http://www.mail-archive.com/linux-omap@vger.kernel.org/msg85932.html

With all these issues around clk inits happening way too early, it
makes sense to at least move them to a point where dynamic memory
allocations are possible. So move them to a point just before the
timer code starts using clocks and hwmod.

This should at least pave way for clk inits on OMAP moving to dynamic
clock registrations instead of using the static macros defined in
clk-private.h.

The issue with kernel panic while CONFIG_DEBUG_SLAB is enabled
was reported by Piotr Haber and Tony Lindgren and this patch
fixes the reported issue as well.

Reported-by: Piotr Haber <phaber@broadcom.com>
Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Paul Walmsley <paul@pwsan.com>
Cc: stable@vger.kernel.org  # v3.8
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/common.h

@@ -293,5 +293,8 @@ extern void omap_reserve(void);
 struct omap_hwmod;
 extern int omap_dss_reset(struct omap_hwmod *);
 
+/* SoC specific clock initializer */
+extern int (*omap_clk_init)(void);
+
 #endif /* __ASSEMBLER__ */
 #endif /* __ARCH_ARM_MACH_OMAP2PLUS_COMMON_H */

arch/arm/mach-omap2/io.c

@@ -54,6 +54,12 @@
 #include "prm3xxx.h"
 #include "prm44xx.h"
 
+/*
+ * omap_clk_init: points to a function that does the SoC-specific
+ * clock initializations
+ */
+int (*omap_clk_init)(void);
+
 /*
  * The machine specific code may provide the extra mapping besides the
  * default mapping provided here.
@@ -397,7 +403,7 @@ void __init omap2420_init_early(void)
 	omap242x_clockdomains_init();
 	omap2420_hwmod_init();
 	omap_hwmod_init_postsetup();
-	omap2420_clk_init();
+	omap_clk_init = omap2420_clk_init;
 }
 
 void __init omap2420_init_late(void)
@@ -427,7 +433,7 @@ void __init omap2430_init_early(void)
 	omap243x_clockdomains_init();
 	omap2430_hwmod_init();
 	omap_hwmod_init_postsetup();
-	omap2430_clk_init();
+	omap_clk_init = omap2430_clk_init;
 }
 
 void __init omap2430_init_late(void)
@@ -462,7 +468,7 @@ void __init omap3_init_early(void)
 	omap3xxx_clockdomains_init();
 	omap3xxx_hwmod_init();
 	omap_hwmod_init_postsetup();
-	omap3xxx_clk_init();
+	omap_clk_init = omap3xxx_clk_init;
 }
 
 void __init omap3430_init_early(void)
@@ -500,7 +506,7 @@ void __init ti81xx_init_early(void)
 	omap3xxx_clockdomains_init();
 	omap3xxx_hwmod_init();
 	omap_hwmod_init_postsetup();
-	omap3xxx_clk_init();
+	omap_clk_init = omap3xxx_clk_init;
 }
 
 void __init omap3_init_late(void)
@@ -568,7 +574,7 @@ void __init am33xx_init_early(void)
 	am33xx_clockdomains_init();
 	am33xx_hwmod_init();
 	omap_hwmod_init_postsetup();
-	am33xx_clk_init();
+	omap_clk_init = am33xx_clk_init;
 }
 #endif
 
@@ -593,7 +599,7 @@ void __init omap4430_init_early(void)
 	omap44xx_clockdomains_init();
 	omap44xx_hwmod_init();
 	omap_hwmod_init_postsetup();
-	omap4xxx_clk_init();
+	omap_clk_init = omap4xxx_clk_init;
 }
 
 void __init omap4430_init_late(void)

arch/arm/mach-omap2/timer.c

@@ -547,6 +547,8 @@ static inline void __init realtime_counter_init(void)
 			       clksrc_nr, clksrc_src)			\
 void __init omap##name##_gptimer_timer_init(void)			\
 {									\
+	if (omap_clk_init)						\
+		omap_clk_init();					\
 	omap_dmtimer_init();						\
 	omap2_gp_clockevent_init((clkev_nr), clkev_src, clkev_prop);	\
 	omap2_gptimer_clocksource_init((clksrc_nr), clksrc_src);	\
@@ -556,6 +558,8 @@ void __init omap##name##_gptimer_timer_init(void)			\
 				clksrc_nr, clksrc_src)			\
 void __init omap##name##_sync32k_timer_init(void)		\
 {									\
+	if (omap_clk_init)						\
+		omap_clk_init();					\
 	omap_dmtimer_init();						\
 	omap2_gp_clockevent_init((clkev_nr), clkev_src, clkev_prop);	\
 	/* Enable the use of clocksource="gp_timer" kernel parameter */	\