• Vaibhav Hiremath's avatar
    ARM: OMAP: Make OMAP clocksource source selection using kernel param · 1fe97c8f
    Vaibhav Hiremath authored
    Current OMAP code supports couple of clocksource options based
    on compilation flag (CONFIG_OMAP_32K_TIMER). The 32KHz sync-timer
    and a gptimer which can run on 32KHz or system clock (e.g 38.4 MHz).
    So there can be 3 options -
    
    1. 32KHz sync-timer
    2. Sys_clock based (e.g 13/19.2/26/38.4 MHz) gptimer
    3. 32KHz based gptimer.
    
    The optional gptimer based clocksource was added so that it can
    give the high precision than sync-timer, so expected usage was 2
    and not 3.
    Unfortunately option 2, clocksource doesn't meet the requirement of
    free-running clock as per clocksource need. It stops in low power states
    when sys_clock is cut. That makes gptimer based clocksource option
    useless for OMAP2/3/4 devices with sys_clock as a clock input.
    So, in order to use option 2, deeper idle state MUST be disabled.
    
    Option 3 will still work but it is no better than 32K sync-timer
    based clocksource.
    
    We must support both sync timer and gptimer based clocksource as
    some OMAP based derivative SoCs like AM33XX does not have the
    sync timer.
    
    Considering above, make sync-timer and gptimer clocksource runtime
    selectable so that both OMAP and AMXXXX continue to use the same code.
    
    And, in order to precisely configure/setup sched_clock for given
    clocksource, decision has to be made early enough in boot sequence.
    
    So, the solution is,
    
    Use standard kernel parameter ("clocksource=") to override
    default 32k_sync-timer, in addition to this, we also use hwmod database
    lookup mechanism, through which at run-time we can identify availability
    of 32k-sync timer on the device, else fall back to gptimer.
    
    Also, moved low-level SoC specific init code to respective files,
    (mach-omap1/timer32k.c and mach-omap2/timer.c)
    Signed-off-by: default avatarVaibhav Hiremath <hvaibhav@ti.com>
    Signed-off-by: default avatarFelipe Balbi <balbi@ti.com>
    Reviewed-by: default avatarSantosh Shilimkar <santosh.shilimkar@ti.com>
    Acked-by: default avatarKevin Hilman <khilman@ti.com>
    Tested-by: default avatarKevin Hilman <khilman@ti.com>
    Cc: Benoit Cousson <b-cousson@ti.com>
    Cc: Paul Walmsley <paul@pwsan.com>
    Cc: Tarun Kanti DebBarma <tarun.kanti@ti.com>
    Cc: Ming Lei <tom.leiming@gmail.com>
    Signed-off-by: default avatarTony Lindgren <tony@atomide.com>
    1fe97c8f
timer.c 14.8 KB