From mboxrd@z Thu Jan 1 00:00:00 1970 From: guy.shapiro@mobi-wize.com (Guy Shapiro) Date: Sun, 22 Jan 2017 12:46:07 +0200 Subject: imx6ul: power-up using the RTC In-Reply-To: <20170120121210.gm3wcg4yyvrigpn3@earth> References: <20170120121210.gm3wcg4yyvrigpn3@earth> Message-ID: <665a40b1-33f5-74bc-49cc-85b01964ae0d@mobi-wize.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 20/01/2017 14:12, 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 | Yes, though I managed to add some useful debug prints while keeping the code broken. > > For me it looks like the debug prints may delay the poweroff driver > long enough, that some other driver (rtc?) writes the 0x0b bits. The problem happens even if I add a long sleep between the RTC setting and the power down command. > > FWIW we can't switch from regmap_write to regmap_update_bits in the > syscon driver, since that may break other users. I guess we need to > introduce a DT property providing the update mask. Unfortunately the > register value property is already named mask :/ I agree. After fixing the bug, I'll start a discussion about this with the DT list.