On Fri, Sep 14, 2012 at 7:37 PM, Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx> wrote: > Shubhrajyoti Datta <omaplinuxkernel@xxxxxxxxx> writes: > >> Hi Kevin, >> >> On Fri, Sep 14, 2012 at 2:15 AM, Kevin Hilman >> <khilman@xxxxxxxxxxxxxxxxxxx> wrote: >>> From: Kevin Hilman <khilman@xxxxxx> >>> >>> 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, >> >>> Cc: Felipe Balbi <balbi@xxxxxx> >>> Cc: Steve Sakoman <steve@xxxxxxxxxxx> >>> Signed-off-by: Kevin Hilman <khilman@xxxxxx> >>> --- >>> 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 > -- 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
