OMAP2/3 GPTIMER: allow system tick GPTIMER to be configurable at build

Add Kbuild code to allow the builder to select which GPTIMER block to use
for the Linux clockevents timer.  Practical choices at this point are
GPTIMER1 or GPTIMER12.  Both of these timers are in the WKUP powerdomain,
and so are unaffected by chip power management.  GPTIMER1 can use sys_clk
as a source, for applications where a high-resolution timer is more important
than power management.  GPTIMER12 has the special property that it has
the secure 32kHz oscillator as its source clock, which may be less prone
to glitches than the off-chip 32kHz oscillator.  But on HS devices, it may
not be available for Linux use.

At this point, it appears that most boards are fine with GPTIMER1, but
Beagle should use GPTIMER12.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

diff --git a/arch/arm/mach-omap2/Kconfig b/arch/arm/mach-omap2/Kconfig
index bb6d695e78f6a0963fe6e528102a483b0d2da09f..365b9826877c0b1d07e99fe56164228d7cdb1e85 100644 (file)
--- a/arch/arm/mach-omap2/Kconfig
+++ b/arch/arm/mach-omap2/Kconfig
@@ -122,3 +122,19 @@ config MACH_OMAP3EVM
 config MACH_OMAP3_BEAGLE
        bool "OMAP3 BEAGLE board"
        depends on ARCH_OMAP3 && ARCH_OMAP34XX
+
+config OMAP_TICK_GPTIMER
+       int "GPTIMER used for system tick timer"
+       depends on ARCH_OMAP2 || ARCH_OMAP3
+       range 1 12
+       default 1
+       help
+         Linux uses one of the twelve on-board OMAP GPTIMER blocks to generate
+         system tick interrupts.  The twelve GPTIMERs have slightly
+         different powerdomain, source clock, and security properties
+         (mostly documented in the OMAP3 TRMs) that can affect the selection
+         of which GPTIMER to use.  The historical default is GPTIMER1.
+         If CONFIG_OMAP_32K_TIMER is selected, Beagle may require GPTIMER12
+         due to hardware sensitivity to glitches on the OMAP 32kHz clock
+         input.
+

diff --git a/arch/arm/mach-omap2/timer-gp.c b/arch/arm/mach-omap2/timer-gp.c
index 557603f99313c9dcf4fef5632fef4c3546ecd892..691a7f8199fe3d1d9b1269b2a9ead883e34cad32 100644 (file)
--- a/arch/arm/mach-omap2/timer-gp.c
+++ b/arch/arm/mach-omap2/timer-gp.c
@@ -99,7 +99,7 @@ static void __init omap2_gp_clockevent_init(void)
 {
        u32 tick_rate;
 
-       gptimer = omap_dm_timer_request_specific(1);
+       gptimer = omap_dm_timer_request_specific(CONFIG_OMAP_TICK_GPTIMER);
        BUG_ON(gptimer == NULL);
 
 #if defined(CONFIG_OMAP_32K_TIMER)
@@ -109,6 +109,9 @@ static void __init omap2_gp_clockevent_init(void)
 #endif
        tick_rate = clk_get_rate(omap_dm_timer_get_fclk(gptimer));
 
+       pr_info("OMAP clockevent source: GPTIMER%d at %u Hz\n",
+               CONFIG_OMAP_TICK_GPTIMER, tick_rate);
+
        omap2_gp_timer_irq.dev_id = (void *)gptimer;
        setup_irq(omap_dm_timer_get_irq(gptimer), &omap2_gp_timer_irq);
        omap_dm_timer_set_int_enable(gptimer, OMAP_TIMER_INT_OVERFLOW);