linux-kernel - Re: [PATCH v2] rtc: OMAP: Add support for rtc-only mode

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Message-ID: <9717549d-29ac-14b9-b8f5-6b39fbbd74e7@ti.com>
Date:   Mon, 9 Jul 2018 15:05:59 +0530
From:   Keerthy <j-keerthy@...com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Johan Hovold <johan@...nel.org>
CC:     <a.zummo@...ertech.it>, <t-kristo@...com>,
        <linux-rtc@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] rtc: OMAP: Add support for rtc-only mode



On Monday 09 July 2018 02:59 PM, Alexandre Belloni wrote:
> On 09/07/2018 09:55:53+0200, Johan Hovold wrote:
>> On Mon, Jul 09, 2018 at 11:41:49AM +0530, Keerthy wrote:
>>> Prepare rtc driver for rtc-only with DDR in self-refresh mode.
>>> omap_rtc_power_off now should cater to two features:
>>>
>>> 1) RTC plus DDR in self-refresh is power a saving mode where in the
>>> entire system including the different voltage rails from PMIC are
>>> shutdown except the ones feeding on to RTC and DDR. DDR is kept in
>>> self-refresh hence the contents are preserved. RTC ALARM2 is connected
>>> to PMIC_EN line once we the ALARM2 is triggered we enter the mode with
>>> DDR in self-refresh and RTC Ticking. After a predetermined time an RTC
>>> ALARM1 triggers waking up the system[1]. The control goes to bootloader.
>>> The bootloader then checks RTC scratchpad registers to confirm it was an
>>> rtc_only wakeup and follows a different path, configure bare minimal
>>> clocks for ddr and then jumps to the resume address in another RTC
>>> scratchpad registers and transfers the control to Kernel. Kernel then
>>> restores the saved context. omap_rtc_power_off_program does the ALARM2
>>> programming part.
>>>
>>>      [1] http://www.ti.com/lit/ug/spruhl7h/spruhl7h.pdf Page 2884
>>>
>>> 2) Power-off: This is usual poweroff mode. omap_rtc_power_off calls the
>>> above omap_rtc_power_off_program function and in addition to that
>>> programs the OMAP_RTC_PMIC_REG for any external wake ups for PMIC like
>>> the pushbutton and shuts off the PMIC.
>>>
>>> Hence the split in omap_rtc_power_off.
>>>
>>> Signed-off-by: Keerthy <j-keerthy@...com>
>>> ---
>>>
>>> Changes in v2:
>>>
>>>   * Add details in the commit log.
>>>   * Use of_device_is_system_power_controller to check if rtc node is
>>>     indeed the system power control instead of manually reading property.
>>>
>>>  drivers/rtc/interface.c |  12 ++++
>>>  drivers/rtc/rtc-omap.c  | 167 +++++++++++++++++++++++++++++++++---------------
>>>  include/linux/rtc.h     |   2 +
>>>  3 files changed, 131 insertions(+), 50 deletions(-)
>>>
>>> diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
>>> index 6d4012d..d8b70f0 100644
>>> --- a/drivers/rtc/interface.c
>>> +++ b/drivers/rtc/interface.c
>>> @@ -1139,3 +1139,15 @@ int rtc_set_offset(struct rtc_device *rtc, long offset)
>>>  	trace_rtc_set_offset(offset, ret);
>>>  	return ret;
>>>  }
>>> +
>>> +/**
>>> + * rtc_power_off_program - Some of the rtc are hooked on to PMIC_EN
>>> + * line and can be used to power off the SoC.
>>> + *
>>> + * Kernel interface to program rtc to power off
>>> + */
>>> +void rtc_power_off_program(struct rtc_device *rtc)
>>> +{
>>> +	rtc->ops->power_off_program(rtc->dev.parent);
>>> +}
>>> +EXPORT_SYMBOL_GPL(rtc_power_off_program);
>>
>> We typically do not add new interfaces without any users, so this will
>> probably have to go in along with the corresponding omap changes for
>> rtc-only mode.
>>
> 
> I'm probably not smart enough but I still don't get why you need to add
> an interface at all, especially one that will result in a NULL pointer
> dereference on 99.6% of the drivers.
> 
> This is so specific to your use case that this has zero chance to be
> reused by another driver.

Alexandre,

So are you suggesting use an EXPORT API from omap-rtc driver alone?
as it is too specific to one use case?

- Keerthy
>