mfd: Clear twl6030 IRQ status register only once

BugLink: http://bugs.launchpad.net/bugs/981162

commit 3f8349e6e98ba0455437724589072523865eae5e upstream.

TWL6030 family of PMIC use a shadow interrupt status register
while kernel processes the current interrupt event.
However, any write(0 or 1) to register INT_STS_A, INT_STS_B or
INT_STS_C clears all 3 interrupt status registers.

Since clear of the interrupt is done on 32k clk, depending on I2C
bus speed, we could in-adverently clear the status of a interrupt
status pending on shadow register in the current implementation.
This is due to the fact that multi-byte i2c write operation into
three seperate status register could result in multiple load
and clear of status and result in lost interrupts.

Instead, doing a single byte write to INT_STS_A register with 0x0
will clear all three interrupt status registers without the related
risk.

Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/drivers/mfd/twl6030-irq.c b/drivers/mfd/twl6030-irq.c
index 3eee45f..83f4988 100644 (file)
--- a/drivers/mfd/twl6030-irq.c
+++ b/drivers/mfd/twl6030-irq.c
@@ -187,8 +187,17 @@ static int twl6030_irq_thread(void *data)
                        }
                local_irq_enable();
                }
-               ret = twl_i2c_write(TWL_MODULE_PIH, sts.bytes,
-                               REG_INT_STS_A, 3); /* clear INT_STS_A */
+
+               /*
+                * NOTE:
+                * Simulation confirms that documentation is wrong w.r.t the
+                * interrupt status clear operation. A single *byte* write to
+                * any one of STS_A to STS_C register results in all three
+                * STS registers being reset. Since it does not matter which
+                * value is written, all three registers are cleared on a
+                * single byte write, so we just use 0x0 to clear.
+                */
+               ret = twl_i2c_write_u8(TWL_MODULE_PIH, 0x00, REG_INT_STS_A);
                if (ret)
                        pr_warning("twl6030: I2C error in clearing PIH ISR\n");