• Kevin Hilman's avatar
    ARM: OMAP2+: WDTIMER integration: fix !PM boot crash, disarm timer after hwmod reset · 414e4128
    Kevin Hilman authored
    Without runtime PM enabled, hwmod needs to leave all IP blocks in an
    enabled state by default so any driver access to the HW will succeed.
    This is accomplished by seting the postsetup_state to enabled for all
    hwmods during init when runtime PM is disabled.
    
    Currently, we have a special case for WDT in that its postsetup_state
    is always set to disabled.  This is done so that the WDT is disabled
    and the timer is disarmed at boot in case there is no WDT driver.
    This also means that when runtime PM is disabled, if a WDT driver *is*
    built in the kernel, the kernel will crash on the first access to the
    WDT hardware.
    
    We can't simply leave the WDT module enabled, because the timer is
    armed by default after reset. That means that if there is no WDT
    driver initialzed or loaded before the timer expires, the kernel will
    reboot.
    
    To fix this, a custom reset method is added to the watchdog class of
    omap_hwmod.  This method will *always* disarm the timer after hwmod
    reset.  The WDT timer then will only be rearmed when/if the driver is
    loaded for the WDT.  With the timer disarmed by default, we no longer
    need a special-case for the postsetup_state of WDT during init, so it
    is removed.
    
    Any platforms wishing to ensure the watchdog remains armed across the
    entire boot boot can simply disable the reset-on-init feature of the
    watchdog hwmod using omap_hwmod_no_setup_reset().
    
    Tested on 3530/Overo, 4430/Panda.
    
    NOTE: on 4430, the hwmod OCP reset does not seem to rearm the timer as
    documented in the TRM (and what happens on OMAP3.)  I noticed this
    because testing the HWMOD_INIT_NO_RESET feature with no driver loaded,
    I expected a reboot part way through the boot, but did not see a
    reboot.  Adding some debug to read the counter, I verified that right
    after OCP softreset, the counter is not firing.  After writing the
    magic start sequence, the timer starts counting.  This means that the
    timer disarm sequence added here does not seem to be needed for 4430,
    but is technically the correct way to ensure the timer is disarmed, so
    it is left in for OMAP4.
    
    Special thanks to Paul Walmsley for helping brainstorm ideas to fix
    this problem.
    
    Cc: Paul Walmsley <paul@pwsan.com>
    Signed-off-by: default avatarKevin Hilman <khilman@ti.com>
    Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
    Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@ti.com>
    [paul@pwsan.com: updated the omap2_wd_timer_reset() function in the
     wake of commit 3c55c1ba ("ARM:
     OMAP2+: hwmod: Revert "ARM: OMAP2+: hwmod: Make omap_hwmod_softreset
     wait for reset status""); added kerneldoc; rolled in warning fix from Kevin]
    Signed-off-by: default avatarPaul Walmsley <paul@pwsan.com>
    414e4128
wd_timer.h 550 Bytes