All of lore.kernel.org
 help / color / mirror / Atom feed
From: Baruch Siach <baruch@tkos.co.il>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/4] rtc: digicolor: set range
Date: Tue, 30 Apr 2019 15:20:08 +0300	[thread overview]
Message-ID: <875zqvu1l3.fsf@tarshish> (raw)
In-Reply-To: <20190430114702.GD11339@piout.net>

Hi Alexandre,

On Tue, Apr 30 2019, Alexandre Belloni wrote:
> On 30/04/2019 14:36:24+0300, Baruch Siach wrote:
>> Hi Alexandre,
>>
>> On Tue, Apr 30 2019, Alexandre Belloni wrote:
>>
>> > While the range of REFERENCE + TIME is actually 33 bits, the counter
>> > itself (TIME) is a 32-bits seconds counter.
>> >
>> > Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
>> > ---
>> >  drivers/rtc/rtc-digicolor.c | 1 +
>> >  1 file changed, 1 insertion(+)
>> >
>> > diff --git a/drivers/rtc/rtc-digicolor.c b/drivers/rtc/rtc-digicolor.c
>> > index 5bb14c56bc9a..e6e16aaac254 100644
>> > --- a/drivers/rtc/rtc-digicolor.c
>> > +++ b/drivers/rtc/rtc-digicolor.c
>> > @@ -206,6 +206,7 @@ static int __init dc_rtc_probe(struct platform_device *pdev)
>> >  	platform_set_drvdata(pdev, rtc);
>> >
>> >  	rtc->rtc_dev->ops = &dc_rtc_ops;
>> > +	rtc->rtc_dev->range_max = U32_MAX;
>>
>> Where can I find documentation on the meaning and usage of the range_max
>> value? I could not find anything in the kernel source.
>
> It should be set to the maximum UNIX timestamp the RTC can be set to
> while keeping range_min to range_max contiguous.
>
> In the digicolor case, you could go up to 8589934590 (Wed Mar 16
> 12:56:30 UTC 2242) but the driver only writes DC_RTC_REFERENCE and I'm
> not sure it can also update DC_RTC_TIME safely.

DC_RTC_TIME resets to zero whenever dc_rtc_write writes CMD_RESET to the
DC_RTC_CONTROL register. DC_RTC_REFERENCE keeps the value that
dc_rtc_write stores there. So the driver will return values larger than
U32_MAX if you happen to cross this point in time between dc_rtc_write
and dc_rtc_read. But you can't store a value larger than U32_MAX in
DC_RTC_REFERENCE.

Will the core RTC code handle the U32_MAX cross correctly?

baruch

--
     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -

WARNING: multiple messages have this Message-ID (diff)
From: Baruch Siach <baruch@tkos.co.il>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/4] rtc: digicolor: set range
Date: Tue, 30 Apr 2019 15:20:08 +0300	[thread overview]
Message-ID: <875zqvu1l3.fsf@tarshish> (raw)
In-Reply-To: <20190430114702.GD11339@piout.net>

Hi Alexandre,

On Tue, Apr 30 2019, Alexandre Belloni wrote:
> On 30/04/2019 14:36:24+0300, Baruch Siach wrote:
>> Hi Alexandre,
>>
>> On Tue, Apr 30 2019, Alexandre Belloni wrote:
>>
>> > While the range of REFERENCE + TIME is actually 33 bits, the counter
>> > itself (TIME) is a 32-bits seconds counter.
>> >
>> > Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
>> > ---
>> >  drivers/rtc/rtc-digicolor.c | 1 +
>> >  1 file changed, 1 insertion(+)
>> >
>> > diff --git a/drivers/rtc/rtc-digicolor.c b/drivers/rtc/rtc-digicolor.c
>> > index 5bb14c56bc9a..e6e16aaac254 100644
>> > --- a/drivers/rtc/rtc-digicolor.c
>> > +++ b/drivers/rtc/rtc-digicolor.c
>> > @@ -206,6 +206,7 @@ static int __init dc_rtc_probe(struct platform_device *pdev)
>> >  	platform_set_drvdata(pdev, rtc);
>> >
>> >  	rtc->rtc_dev->ops = &dc_rtc_ops;
>> > +	rtc->rtc_dev->range_max = U32_MAX;
>>
>> Where can I find documentation on the meaning and usage of the range_max
>> value? I could not find anything in the kernel source.
>
> It should be set to the maximum UNIX timestamp the RTC can be set to
> while keeping range_min to range_max contiguous.
>
> In the digicolor case, you could go up to 8589934590 (Wed Mar 16
> 12:56:30 UTC 2242) but the driver only writes DC_RTC_REFERENCE and I'm
> not sure it can also update DC_RTC_TIME safely.

DC_RTC_TIME resets to zero whenever dc_rtc_write writes CMD_RESET to the
DC_RTC_CONTROL register. DC_RTC_REFERENCE keeps the value that
dc_rtc_write stores there. So the driver will return values larger than
U32_MAX if you happen to cross this point in time between dc_rtc_write
and dc_rtc_read. But you can't store a value larger than U32_MAX in
DC_RTC_REFERENCE.

Will the core RTC code handle the U32_MAX cross correctly?

baruch

--
     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2019-04-30 12:20 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-30  9:32 [PATCH 1/4] rtc: digicolor: fix possible race condition Alexandre Belloni
2019-04-30  9:32 ` Alexandre Belloni
2019-04-30  9:32 ` [PATCH 2/4] rtc: digicolor: set range Alexandre Belloni
2019-04-30  9:32   ` Alexandre Belloni
2019-04-30 11:36   ` Baruch Siach
2019-04-30 11:36     ` Baruch Siach
2019-04-30 11:47     ` Alexandre Belloni
2019-04-30 11:47       ` Alexandre Belloni
2019-04-30 12:20       ` Baruch Siach [this message]
2019-04-30 12:20         ` Baruch Siach
2019-04-30 13:05         ` Alexandre Belloni
2019-04-30 13:05           ` Alexandre Belloni
2019-04-30 15:25           ` Baruch Siach
2019-04-30 15:25             ` Baruch Siach
2019-04-30 19:10             ` Alexandre Belloni
2019-04-30 19:10               ` Alexandre Belloni
2019-04-30  9:32 ` [PATCH 3/4] rtc: digicolor: use .set_time Alexandre Belloni
2019-04-30  9:32   ` Alexandre Belloni
2019-04-30 12:21   ` Baruch Siach
2019-04-30 12:21     ` Baruch Siach
2019-04-30  9:32 ` [PATCH 4/4] rtc: digicolor: convert to SPDX identifier Alexandre Belloni
2019-04-30  9:32   ` Alexandre Belloni
2019-04-30 12:22   ` Baruch Siach
2019-04-30 12:22     ` Baruch Siach
2019-04-30 11:25 ` [PATCH 1/4] rtc: digicolor: fix possible race condition Baruch Siach
2019-04-30 11:25   ` Baruch Siach

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=875zqvu1l3.fsf@tarshish \
    --to=baruch@tkos.co.il \
    --cc=alexandre.belloni@bootlin.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rtc@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.