From mboxrd@z Thu Jan 1 00:00:00 1970 From: sre@kernel.org (Sebastian Reichel) Date: Fri, 20 Jan 2017 13:12:10 +0100 Subject: imx6ul: power-up using the RTC In-Reply-To: References: Message-ID: <20170120121210.gm3wcg4yyvrigpn3@earth> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. 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 :/ -- Sebastian -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 833 bytes Desc: not available URL: