From mboxrd@z Thu Jan 1 00:00:00 1970 From: alexandre.belloni@free-electrons.com (Alexandre Belloni) Date: Fri, 20 Jan 2017 16:34:59 +0100 Subject: imx6ul: power-up using the RTC In-Reply-To: <20170120121210.gm3wcg4yyvrigpn3@earth> References: <20170120121210.gm3wcg4yyvrigpn3@earth> Message-ID: <20170120153459.tewyg54dcgqnpz2j@piout.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 20/01/2017 at 13:12:10 +0100, Sebastian Reichel wrote : > Hi, > > On Wed, Jan 18, 2017 at 04:49:11PM +0200, Guy Shapiro wrote: > > I'm trying to use the low power RTC of the i.MX6UL to start from > > power-off state. > > > > I started by hopefully running: # echo +30 > > > /sys/class/rtc/rtc0/wakealarm && shutdown -h now The system was > > powered down, but it didn't come up after 30 seconds as expected. > > > > So I dug into the datasheet and the source... > > To activate the power on alarm, the flags SRTC_ENV, LPTA_EN and LPWUI_EN on > > the SNVS_LP Control register (LPCR) should be asserted. The wakeup time > > should be written to the SNVS_LP Time alarm register (LPTA). The code that > > does this is on drivers/rtc/rtc-snvs.c:snvs_rtc_set_alarm(). > > > > The first problem I found was with the use of the syscon-poweroff driver. > > The "Turn off System Power" flag is part of the same register (LPCR). The > > current code of syscon-poweroff set the register to the "mask" property from > > the device tree on power off, overriding all the existing flags. > > After setting the "mask" property on the device tree to 0x6b instead of > > 0x60 (asserting the mentioned bits), the system do power up on timer, as > > expected. > > > > However, I didn't like the idea of keeping those flags on even when no one > > set the alarm. > > As a quick test, I modified the syscon-poweroff driver to ignore the bits > > that are not on the mask: > > > > diff --git a/drivers/power/reset/syscon-poweroff.c > > b/drivers/power/reset/syscon-poweroff.c > > index b683383..a5da02b 100644 > > --- a/drivers/power/reset/syscon-poweroff.c > > +++ b/drivers/power/reset/syscon-poweroff.c > > @@ -33,7 +33,7 @@ static u32 mask; > > static void syscon_poweroff(void) > > { > > /* Issue the poweroff */ > > - regmap_write(map, offset, mask); > > + regmap_update_bits(map, offset, mask, mask); > > mdelay(1000); > > > > > > After applying this fix, the wake up alarm didn't work. Strangely, when I > > added some debug prints to investigate the case, it worked again > > (sometimes... depends on the exact places I add the prints). > > I suspect that some other driver clears the flags during the power down, but > > I couldn't find such driver. > > > > Do you have any clue what code may change this register during the shutdown > > process? Any other insights are welcomed as well :) > > To summarize it looks like this? > > | regmap_write | 0x60 | broken | > | regmap_write | 0x6b | works stable | > | regmap_update_bits | 0x60 | works only with dbg prints | > > For me it looks like the debug prints may delay the poweroff driver > long enough, that some other driver (rtc?) writes the 0x0b bits. > Is snvs_rtc_alarm_irq_enable() waiting long enough? I'd say yes but you never know... You can also use the kernel tracin infrastructure to trace every accesses made to that regmap. That could give you a hint. At least you can try a regmap_read before returning from snvs_rtc_alarm_irq_enable() and see whether SNVS_LPCR_LPTA_EN and SNVS_LPCR_LPWUI_EN are still there. -- Alexandre Belloni, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com