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OMAP3: PM: Prevent hang in prcm_interrupt_handler
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There are two scenarios where a race condition could result in a hang
in the prcm_interrupt handler. These are:

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.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
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Jon Hunter authored and Kevin Hilman committed Oct 5, 2009
1 parent 17d857b commit 77da2d9
Showing 1 changed file with 60 additions and 83 deletions.
143 changes: 60 additions & 83 deletions arch/arm/mach-omap2/pm34xx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,97 +51,74 @@ static void (*_omap_sram_idle)(u32 *addr, int save_state);

static struct powerdomain *mpu_pwrdm;

/* PRCM Interrupt Handler for wakeups */
static irqreturn_t prcm_interrupt_handler (int irq, void *dev_id)
/*
* PRCM Interrupt Handler Helper Function
*
* The purpose of this function is to clear any wake-up events latched
* in the PRCM PM_WKST_x registers. It is possible that a wake-up event
* may occur whilst attempting to clear a PM_WKST_x register and thus
* set another bit in this register. A while loop is used to ensure
* that any peripheral wake-up events occurring while attempting to
* clear the PM_WKST_x are detected and cleared.
*/
static void prcm_clear_mod_irqs(s16 module, u8 regs)
{
u32 wkst, irqstatus_mpu;
u32 fclk, iclk;
u32 wkst, fclk, iclk;
u16 wkst_off = (regs == 3) ? OMAP3430ES2_PM_WKST3 : PM_WKST1;
u16 fclk_off = (regs == 3) ? OMAP3430ES2_CM_FCLKEN3 : CM_FCLKEN1;
u16 iclk_off = (regs == 3) ? CM_ICLKEN3 : CM_ICLKEN1;

/* WKUP */
wkst = prm_read_mod_reg(WKUP_MOD, PM_WKST);
wkst = prm_read_mod_reg(module, wkst_off);
if (wkst) {
iclk = cm_read_mod_reg(WKUP_MOD, CM_ICLKEN);
fclk = cm_read_mod_reg(WKUP_MOD, CM_FCLKEN);
cm_set_mod_reg_bits(wkst, WKUP_MOD, CM_ICLKEN);
cm_set_mod_reg_bits(wkst, WKUP_MOD, CM_FCLKEN);
prm_write_mod_reg(wkst, WKUP_MOD, PM_WKST);
while (prm_read_mod_reg(WKUP_MOD, PM_WKST))
cpu_relax();
cm_write_mod_reg(iclk, WKUP_MOD, CM_ICLKEN);
cm_write_mod_reg(fclk, WKUP_MOD, CM_FCLKEN);
}

/* CORE */
wkst = prm_read_mod_reg(CORE_MOD, PM_WKST1);
if (wkst) {
iclk = cm_read_mod_reg(CORE_MOD, CM_ICLKEN1);
fclk = cm_read_mod_reg(CORE_MOD, CM_FCLKEN1);
cm_set_mod_reg_bits(wkst, CORE_MOD, CM_ICLKEN1);
cm_set_mod_reg_bits(wkst, CORE_MOD, CM_FCLKEN1);
prm_write_mod_reg(wkst, CORE_MOD, PM_WKST1);
while (prm_read_mod_reg(CORE_MOD, PM_WKST1))
cpu_relax();
cm_write_mod_reg(iclk, CORE_MOD, CM_ICLKEN1);
cm_write_mod_reg(fclk, CORE_MOD, CM_FCLKEN1);
}
wkst = prm_read_mod_reg(CORE_MOD, OMAP3430ES2_PM_WKST3);
if (wkst) {
iclk = cm_read_mod_reg(CORE_MOD, CM_ICLKEN3);
fclk = cm_read_mod_reg(CORE_MOD, OMAP3430ES2_CM_FCLKEN3);
cm_set_mod_reg_bits(wkst, CORE_MOD, CM_ICLKEN3);
cm_set_mod_reg_bits(wkst, CORE_MOD, OMAP3430ES2_CM_FCLKEN3);
prm_write_mod_reg(wkst, CORE_MOD, OMAP3430ES2_PM_WKST3);
while (prm_read_mod_reg(CORE_MOD, OMAP3430ES2_PM_WKST3))
cpu_relax();
cm_write_mod_reg(iclk, CORE_MOD, CM_ICLKEN3);
cm_write_mod_reg(fclk, CORE_MOD, OMAP3430ES2_CM_FCLKEN3);
}

/* PER */
wkst = prm_read_mod_reg(OMAP3430_PER_MOD, PM_WKST);
if (wkst) {
iclk = cm_read_mod_reg(OMAP3430_PER_MOD, CM_ICLKEN);
fclk = cm_read_mod_reg(OMAP3430_PER_MOD, CM_FCLKEN);
cm_set_mod_reg_bits(wkst, OMAP3430_PER_MOD, CM_ICLKEN);
cm_set_mod_reg_bits(wkst, OMAP3430_PER_MOD, CM_FCLKEN);
prm_write_mod_reg(wkst, OMAP3430_PER_MOD, PM_WKST);
while (prm_read_mod_reg(OMAP3430_PER_MOD, PM_WKST))
cpu_relax();
cm_write_mod_reg(iclk, OMAP3430_PER_MOD, CM_ICLKEN);
cm_write_mod_reg(fclk, OMAP3430_PER_MOD, CM_FCLKEN);
iclk = cm_read_mod_reg(module, iclk_off);
fclk = cm_read_mod_reg(module, fclk_off);
while (wkst) {
cm_set_mod_reg_bits(wkst, module, iclk_off);
cm_set_mod_reg_bits(wkst, module, fclk_off);
prm_write_mod_reg(wkst, module, wkst_off);
wkst = prm_read_mod_reg(module, wkst_off);
}
cm_write_mod_reg(iclk, module, iclk_off);
cm_write_mod_reg(fclk, module, fclk_off);
}
}

if (omap_rev() > OMAP3430_REV_ES1_0) {
/* USBHOST */
wkst = prm_read_mod_reg(OMAP3430ES2_USBHOST_MOD, PM_WKST);
if (wkst) {
iclk = cm_read_mod_reg(OMAP3430ES2_USBHOST_MOD,
CM_ICLKEN);
fclk = cm_read_mod_reg(OMAP3430ES2_USBHOST_MOD,
CM_FCLKEN);
cm_set_mod_reg_bits(wkst, OMAP3430ES2_USBHOST_MOD,
CM_ICLKEN);
cm_set_mod_reg_bits(wkst, OMAP3430ES2_USBHOST_MOD,
CM_FCLKEN);
prm_write_mod_reg(wkst, OMAP3430ES2_USBHOST_MOD,
PM_WKST);
while (prm_read_mod_reg(OMAP3430ES2_USBHOST_MOD,
PM_WKST))
cpu_relax();
cm_write_mod_reg(iclk, OMAP3430ES2_USBHOST_MOD,
CM_ICLKEN);
cm_write_mod_reg(fclk, OMAP3430ES2_USBHOST_MOD,
CM_FCLKEN);
/*
* PRCM Interrupt Handler
*
* The PRM_IRQSTATUS_MPU register indicates if there are any pending
* interrupts from the PRCM for the MPU. These bits must be cleared in
* order to clear the PRCM interrupt. The PRCM interrupt handler is
* implemented to simply clear the PRM_IRQSTATUS_MPU in order to clear
* the PRCM interrupt. Please note that bit 0 of the PRM_IRQSTATUS_MPU
* register indicates that a wake-up event is pending for the MPU and
* this bit can only be cleared if the all the wake-up events latched
* in the various PM_WKST_x registers have been cleared. The interrupt
* handler is implemented using a do-while loop so that if a wake-up
* event occurred during the processing of the prcm interrupt handler
* (setting a bit in the corresponding PM_WKST_x register and thus
* preventing us from clearing bit 0 of the PRM_IRQSTATUS_MPU register)
* this would be handled.
*/
static irqreturn_t prcm_interrupt_handler (int irq, void *dev_id)
{
u32 irqstatus_mpu;

do {
prcm_clear_mod_irqs(WKUP_MOD, 1);
prcm_clear_mod_irqs(CORE_MOD, 1);
prcm_clear_mod_irqs(OMAP3430_PER_MOD, 1);
if (omap_rev() > OMAP3430_REV_ES1_0) {
prcm_clear_mod_irqs(CORE_MOD, 3);
prcm_clear_mod_irqs(OMAP3430ES2_USBHOST_MOD, 1);
}
}

irqstatus_mpu = prm_read_mod_reg(OCP_MOD,
OMAP3_PRM_IRQSTATUS_MPU_OFFSET);
prm_write_mod_reg(irqstatus_mpu, OCP_MOD,
OMAP3_PRM_IRQSTATUS_MPU_OFFSET);
irqstatus_mpu = prm_read_mod_reg(OCP_MOD,
OMAP3_PRM_IRQSTATUS_MPU_OFFSET);
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();
} while (prm_read_mod_reg(OCP_MOD, OMAP3_PRM_IRQSTATUS_MPU_OFFSET));

return IRQ_HANDLED;
}
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