Vikram Pandita <[email protected]> writes: > 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/[email protected]/msg13786.html
I much prefer Jon's version, which also added some additional needed cleanup and removed lots of code duplication, but may need some additional tweaking to support the special-case raised in your USBHOST patch. Kevin > Signed-off-by: Vikram Pandita <[email protected]> > cc: Hunter, Jon <[email protected]> > --- > 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
