[PATCH] RTC: TWL: ensure all interrupts are disabled during probe

On Fri, Sep 14, 2012 at 7:37 PM, Kevin Hilman
[off-list ref] wrote:

Shubhrajyoti Datta [off-list ref] writes:

quoted

Hi Kevin,

On Fri, Sep 14, 2012 at 2:15 AM, Kevin Hilman
[off-list ref] wrote:

quoted

From: Kevin Hilman <redacted>

On some platforms, bootloaders are known to do some interesting RTC
programming.  Without going into the obscurities as to why this may be
the case, suffice it to say the the driver should not make any
assumptions about the state of the RTC when the driver loads.  In
particular, the driver probe should be sure that all interrupts are
disabled until otherwise programmed.

This was discovered when finding bursty I2C traffic every second on
Overo platforms.  This I2C overhead was keeping the SoC from hitting
deep power states.  The cause was found to be the RTC firing every
second on the I2C-connected TWL PMIC.

Special thanks to Felipe Balbi for suggesting to look for a rogue
driver as the source of the I2C traffic rather than the I2C driver
itself.

Special thanks to Steve Sakoman for helping track down the source of
the continuous RTC interrups on the Overo boards.

Tested that the continuous interrupt issue after doing a i2c mm on omap4sdp.
This patch solves the issue.
thanks,

quoted

Cc: Felipe Balbi <redacted>
Cc: Steve Sakoman <redacted>
Signed-off-by: Kevin Hilman <redacted>
---
Patch applies to v3.6-rc5

 drivers/rtc/rtc-twl.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/rtc/rtc-twl.c b/drivers/rtc/rtc-twl.c
index c5d06fe..9277d94 100644
--- a/drivers/rtc/rtc-twl.c
+++ b/drivers/rtc/rtc-twl.c

@@ -495,6 +495,11 @@ static int __devinit twl_rtc_probe(struct platform_device *pdev)
        if (ret < 0)
                goto out1;

+       /* ensure interrupts are disabled, bootloaders can be strange */
+       ret = twl_rtc_write_u8(0, REG_RTC_INTERRUPTS_REG);
+       if (ret < 0)
+               dev_warn(&pdev->dev, "unable to disable interrupt\n");
+

Now that it is always 0 can the below read be removed as it is redundant now.

Possibly, but I don't know this HW well enough to know if there are any
persistent bits in that register on any of the various derivations of
this PMIC.  Since this read-back value is used throughout the driver, I
decided not to mess with it when doing this targetted fix.

Indeed makes sense.

Kevin