There are two scenarios where a race condition could result in a hang in the prcm_interrupt handler: 1) Waiting for PRM_IRQSTATUS_MPU register to clear. Bit 0 of the PRM_IRQSTATUS_MPU register indicates that a wake-up event is pending for the MPU. This bit can only be cleared if the all the wake-up events latched in the various PM_WKST_x registers have been cleared. If a wake-up event occurred during the processing of the prcm interrupt handler, after the corresponding PM_WKST_x register was checked but before the PRM_IRQSTATUS_MPU was cleared, then the CPU would be stuck forever waiting for bit 0 in PRM_IRQSTATUS_MPU to be cleared. 2) Waiting for the PM_WKST_x register to clear. Some power domains have more than one wake-up source. The PM_WKST_x registers indicate the source of a wake-up event and need to be cleared after a wake-up event occurs. When the PM_WKST_x registers are read and before they are cleared, it is possible that another wake-up event could occur causing another bit to be set in one of the PM_WKST_x registers. If this did occur after reading a PM_WKST_x register then the CPU would miss this event and get stuck forever in a loop waiting for that PM_WKST_x register to clear. This patch address the above race conditions that would result in a hang. Adapted from a version posted by Jon Hunter: http://www.mail-archive.com/linux-omap@xxxxxxxxxxxxxxx/msg13786.html Signed-off-by: Vikram Pandita <vikram.pandita@xxxxxx> cc: Hunter, Jon <jon-hunter@xxxxxx> --- arch/arm/mach-omap2/pm34xx.c | 11 +++++++++-- 1 files changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/arm/mach-omap2/pm34xx.c b/arch/arm/mach-omap2/pm34xx.c index 4cbeff1..ce34ac1 100644 --- a/arch/arm/mach-omap2/pm34xx.c +++ b/arch/arm/mach-omap2/pm34xx.c @@ -200,6 +200,10 @@ static irqreturn_t prcm_interrupt_handler (int irq, void *dev_id) u32 wkst, irqstatus_mpu; u32 fclk, iclk; +restart: + fclk = 0; + iclk = 0; + /* WKUP */ wkst = prm_read_mod_reg(WKUP_MOD, PM_WKST); if (wkst) { @@ -285,8 +289,11 @@ static irqreturn_t prcm_interrupt_handler (int irq, void *dev_id) prm_write_mod_reg(irqstatus_mpu, OCP_MOD, OMAP3_PRM_IRQSTATUS_MPU_OFFSET); - while (prm_read_mod_reg(OCP_MOD, OMAP3_PRM_IRQSTATUS_MPU_OFFSET)) - cpu_relax(); + /* In case another wakep happend while in this handler, + * restart the clearing process + */ + if (prm_read_mod_reg(OCP_MOD, OMAP3_PRM_IRQSTATUS_MPU_OFFSET)) + goto restart; return IRQ_HANDLED; } -- 1.6.3.3.334.g916e1 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
