[rtc-linux] Re: Intersil ISL12057 driver

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

On 25/03/2016 at 22:58:40 +0100, Arnaud Ebalard wrote :
> Hi Alexandre,
> 
> Alexandre Belloni <alexandre.belloni@free-electrons.com> writes:
> 
> > On 24/03/2016 at 23:26:24 +0100, Arnaud Ebalard wrote :
> >> 1) Handling of the century bit
> >> 
> >
> > This indeed needs fixing and it is quite simple. Do you care sending a
> > patch?
> 
> A first version is below. As discussed in the commit message, it is
> trivial to make set_ and get_ time functions consistent. But it is not
> that easy to extend the capabilities of the driver after 2099 w/o
> breaking current platforms.
> 
> Basically, the patch below simply remove support for century bit for
> ds1307 flavours that have the feature to get things consistent. A sanity
> check is also added.
> 

Well, we are still a few years away from the cutoff date so we can
probably transition properly. However, some systems (like Android) need
support for date between 1970 and 2000. So I'll need to think a bit more
about it.

> Comments welcome!
> 
> >> 2) Alarm:
> >> 
> >
> > [...]
> >
> > Well, my bad, your analysis is correct and I was thinking
> > 8bc2a40730ec74271a0573a6882871308d069f5d was in 4.5 but it will actually
> > be in 4.6:
> > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8bc2a40730ec74271a0573a6882871308d069f5d
> >
> > This should solve that one. And you are right, I should probably do
> > something more generic in the framework to handle "wakeup-source".
> 
> I have tested a 4.5 with 8bc2a40730ec74 and alarm support works as
> expected (i.e. wakeup-source property from dts is honored).
> 
> The only minor things to address before removing my (regmap-enabled ;-))

Yeah, your driver is clearly cleaner I waiting to get get some of those
dallas RTCs to clean the ds1307 driver.

> rtc-isl12057.c driver from the tree is the backward compatibility for
> "isil,isl12057", "isl,isl12057" and "isil,irq2-can-wakeup-machine" that
> may be in existing .dtb and the drivcer support.
> 
> Regarding in-kernel users (RN102, RN104 and RN2120), those devices came
> with a non-dt capable u-boot; the kernels are ones with an appended dtb,
> which is usually updated w/ the kernel. For thoses ones, I do not think
> there is any need for retrocompatibility.
> 

Well, if you don't think "isil,irq2-can-wakeup-machine" is needed for
backward compatibility, I'd let it out but I would still add "isl12057" to
the ds1307_id table. This will add support for both compatible strings.

> Thoughts?
> 
> Cheers,
> 
> a+
> 
> 
> From 4af5d133daf3a77a39c2f0c17b245ed622e20c16 Mon Sep 17 00:00:00 2001
> From: Arnaud Ebalard <arno@natisbad.org>
> Date: Fri, 25 Mar 2016 21:21:09 +0100
> Subject: [PATCH] rtc: ds1307: fix inconsistent use of century bit
> 
> Historically, ds1307 RTC driver mistakenly enabled century
> bit when setting the time between 2000 and 2099 (on century
> supporting flavour i.e. ds1337, ds1339, ds3231 and ds1340), but
> ignored it when reading the time. In practice, this prevents the
> driver to support time values after 2099.
> 
> This commit removes support for century bit for century capable
> flavours supported by the driver to make get and set function
> consistent. It also adds an explicit check that passed year
> values are in the right range when setting time.
> 
> Note that it is not possible to make the driver support time
> values after 2099 in a way compatible with currently deployed
> versions because RTC chips in the field now have their century
> bit set.
> ---
>  drivers/rtc/rtc-ds1307.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
> index b2156ee5bae1..1537ec83bf8e 100644
> --- a/drivers/rtc/rtc-ds1307.c
> +++ b/drivers/rtc/rtc-ds1307.c
> @@ -413,20 +413,12 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
>  	buf[DS1307_REG_MONTH] = bin2bcd(t->tm_mon + 1);
>  
>  	/* assume 20YY not 19YY */
> +	if (t->tm_year < 100 || t->tm_year > 199)
> +		return -EINVAL;
>  	tmp = t->tm_year - 100;
>  	buf[DS1307_REG_YEAR] = bin2bcd(tmp);
>  
>  	switch (ds1307->type) {
> -	case ds_1337:
> -	case ds_1339:
> -	case ds_3231:
> -		buf[DS1307_REG_MONTH] |= DS1337_BIT_CENTURY;
> -		break;
> -	case ds_1340:
> -		buf[DS1307_REG_HOUR] |= DS1340_BIT_CENTURY_EN
> -				| DS1340_BIT_CENTURY;
> -		break;
>  	case mcp794xx:
>  		/*
>  		 * these bits were cleared when preparing the date/time
> -- 
> 2.7.0
> 

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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