linux-kernel - Re: [PATCH] rtc: ds1307: fix ds1339 wakealarm support

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Message-ID: <20181022155224.GS17341@piout.net>
Date:   Mon, 22 Oct 2018 17:52:24 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Soeren Moch <smoch@....de>
Cc:     stable@...r.kernel.org, Andrea Greco <a.greco@...gma.it>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: ds1307: fix ds1339 wakealarm support

On 22/10/2018 16:18:13+0200, Soeren Moch wrote:
> Hi,
> 
> Am 22.10.2018 um 15:57 schrieb Alexandre Belloni:
> > Hello,
> >
> > On 22/10/2018 14:38:12+0200, Soeren Moch wrote:
> >> Commit 51ed73eb998a1c79a2b0e9bed68f75a8a2c93b9b ("rtc: ds1340: Add support
> >> for trickle charger.") breaks ds1339 wakealarm support by limiting
> >> accessible registers. Fix this.
> >>
> >> Fixes: 51ed73eb998a ("rtc: ds1340: Add support for trickle charger.")
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Soeren Moch <smoch@....de>
> >> --
> >> Cc: Andrea Greco <a.greco@...gma.it>
> >> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> >> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> >> Cc: linux-rtc@...r.kernel.org
> >> Cc: linux-kernel@...r.kernel.org
> >> ---
> >>  drivers/rtc/rtc-ds1307.c | 1 -
> >>  1 file changed, 1 deletion(-)
> >>
> >> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
> >> index 4b2b4627daeb..71396b62dc52 100644
> >> --- a/drivers/rtc/rtc-ds1307.c
> >> +++ b/drivers/rtc/rtc-ds1307.c
> >> @@ -1384,7 +1384,6 @@ static void ds1307_clks_register(struct ds1307 *ds1307)
> >>  static const struct regmap_config regmap_config = {
> >>  	.reg_bits = 8,
> >>  	.val_bits = 8,
> >> -	.max_register = 0x9,
> > I would prefer having a different regmap_config for chips that have more
> > registers. I guess you could put a pointer to a regmap_config in chip_desc.
> >
> What looks strange to me, the original patch (according to its
> description) enabled trickle charger functionality for a single chip.
> This is something totally different than limiting the register space for
> all chips that are supported by this driver. So this seems to be an
> accident to me. And this causes an regression for ds1339, which was
> supported for years.
> 
> Are there any advantages for limiting the address space of i2c devices?

I would think it was done as a facility to debug the feature because
when max_register is set, regmap will allow you to dump the register
space.

> If we really need this, can we apply this partial revert as regression
> fix (also for stable) and implement the address space limitation separately?
> 

Fine, I'm applying this patch right now.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com