linux-kernel - Re: [PATCH] drivers/rtc/rtc-palmas.c: support for backup battery charging

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130726155257.GB3528@e106331-lin.cambridge.arm.com>
Date:	Fri, 26 Jul 2013 16:52:57 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Laxman Dewangan <ldewangan@...dia.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	"gg@...mlogic.co.uk" <gg@...mlogic.co.uk>,
	"kishon@...com" <kishon@...com>,
	Stephen Warren <swarren@...dia.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [PATCH] drivers/rtc/rtc-palmas.c: support for backup battery
 charging

On Fri, Jul 26, 2013 at 04:40:15PM +0100, Stephen Warren wrote:
> (CC'ing the new DT binding maintainers and mailing list on this reply,
> hence quoting the whole of the DT binding)

Thanks Stephen.

> 
> On 07/25/2013 06:29 AM, Laxman Dewangan wrote:
> > Palmas series device like TPS65913, TPS80036 supports the backup battery
> > for powering the RTC when no other energy source is available.
> > 
> > The backup battery is optional, connected to the VBACKUP pin, and can be
> > nonrechargeable or rechargeable. The rechargeable battery can be charged
> > from the system supply using the backup battery charger.
> > 
> > Add support for enabling charging of this backup battery.  Also add the DT
> > binding document and the new properties to have this support.
> > 
> > Signed-off-by: Laxman Dewangan <ldewangan@...dia.com>
> > ---
> >  .../devicetree/bindings/rtc/rtc-palmas.txt         |   28 ++++++++++++++
> >  drivers/rtc/rtc-palmas.c                           |   39 ++++++++++++++++++++
> >  2 files changed, 67 insertions(+), 0 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/rtc/rtc-palmas.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/rtc/rtc-palmas.txt b/Documentation/devicetree/bindings/rtc/rtc-palmas.txt
> > new file mode 100644
> > index 0000000..e4b6910
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/rtc/rtc-palmas.txt
> > @@ -0,0 +1,28 @@
> > +Palmas RTC controller bindings
> > +
> > +Required properties:
> > +- compatible:
> > +  - "ti,palams-rtc" for palma series of the RTC controller
> > +- interrupt-parent: Parent interrupt device, must be handle of palams node.
> > +- interrupts: Interrupt number of RTC submodule on device.
> > +
> > +Optional properties:
> > +- ti,back-bat-chg-enable: The palmas series device like TPS65913 or TPS80036
> > +	supports the battery backup for powering the RTC when main battery is
> > +	removed or in very low power state. This flag will enable the backup
> > +	battery charging.

Perhaps "ti,has-rechargeable-battery" would be better, as this describes
the hardware rather than an intent relating to it.

> > +- ti,back-bat-chg-current: Configure charging current. Device supports the
> > +	charging current as < 100mA or >100mA.

Are either of these values unsafe or unsupported in some configurations?

> 
> Does the HW support just two options; less-than or greater-than 100mA?
> If so, a Boolean property here might be better. The code below certainly
> implies this.
> 
> Given there's only 1 battery, I think "back-" is redundant in the
> property names. Since that shortens the names a bit, I'd suggest
> spelling everything out in full, perhaps:
> 
> battery-charge-enable
> battery-charge-low-current
> 
> Both Boolean.
> 
> > +Example:
> > +	palmas: tps65913@58 {
> > +		:::::::::::
> 
> "..." is probably more common than lots of colons, or you could just
> delete this line.
> 
> > +		palmas_rtc: rtc {
> > +			compatible = "ti,palmas-rtc";
> > +			interrupt-parent = <&palmas>;
> > +			interrupts = <8 0>;
> > +			ti,back-bat-chg-enable;
> > +			ti,back-bat-chg-current = <100>;
> > +		};
> > +		:::::::::::
> > +	};
> 
> > diff --git a/drivers/rtc/rtc-palmas.c b/drivers/rtc/rtc-palmas.c
> 
> > @@ -238,6 +238,19 @@ static int palmas_rtc_probe(struct platform_device *pdev)
> 
> > +		ret = of_property_read_u32(pdev->dev.of_node,
> > +					"ti,back-bat-chg-current", &pval);
> > +		if (!ret)
> > +			bb_charging_current = pval;
> 
> Do you need to validate that pval is one of the legal values?
> 
> > @@ -254,6 +267,32 @@ static int palmas_rtc_probe(struct platform_device *pdev)
> >  	palmas_rtc->dev = &pdev->dev;
> >  	platform_set_drvdata(pdev, palmas_rtc);
> >  
> > +	if (enable_bb_charging) {
> > +		unsigned reg = 0;
> > +
> > +		if (bb_charging_current < 100)
> > +			reg |= PALMAS_BACKUP_BATTERY_CTRL_BBS_BBC_LOW_ICHRG;
> 
> This implies that a Boolean property would be a better representation of HW.
> 

Otherwise, +1 to Stephen's comments.

Thanks,
Mark.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/