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Date: Thu, 28 Aug 2014 10:40:34 -0700 From: Guenter Roeck <linux@...ck-us.net> To: Jason Cooper <jason@...edaemon.net> Cc: Mark Rutland <mark.rutland@....com>, Matti Vaittinen <matti.vaittinen@....com>, "a.zummo@...ertech.it" <a.zummo@...ertech.it>, "jic23@...nel.org" <jic23@...nel.org>, "arno@...isbad.org" <arno@...isbad.org>, "jgunthorpe@...idianresearch.com" <jgunthorpe@...idianresearch.com>, "san@...etechnology.dk" <san@...etechnology.dk>, "hs@...x.de" <hs@...x.de>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>, Sverdlin Alexander <alexander.sverdlin@....com> Subject: Re: [PATCH] rtc: ds1307: add trickle charger device tree binding On Thu, Aug 28, 2014 at 01:28:42PM -0400, Jason Cooper wrote: > On Thu, Aug 28, 2014 at 09:48:25AM -0700, Guenter Roeck wrote: > > On Thu, Aug 28, 2014 at 05:10:25PM +0100, Mark Rutland wrote: > > > On Thu, Aug 28, 2014 at 04:51:57PM +0100, Guenter Roeck wrote: > > > > On Thu, Aug 28, 2014 at 01:59:15PM +0100, Mark Rutland wrote: > > > > > On Thu, Aug 28, 2014 at 01:42:44PM +0100, Matti Vaittinen wrote: > > > > > > Patch adding support for specifying trickle charger setup from device > > > > > > tree. Patch is based on linux-next tree. > > > > > > > > > > > > > > > > > > Some DS13XX devices have "trickle chargers". Introduce a device tree binding > > > > > > for specifying the setup and register values. > > > > > > > > > > > > Signed-off-by: Matti Vaittinen <matti.vaittinen@....com> > > > > > > --- > > > > > > .../devicetree/bindings/i2c/trivial-devices.txt | 1 - > > > > > > .../devicetree/bindings/rtc/dallas,ds1339.txt | 19 ++++++++++ > > > > > > drivers/rtc/rtc-ds1307.c | 44 ++++++++++++++++++++-- > > > > > > 3 files changed, 59 insertions(+), 5 deletions(-) > > > > > > create mode 100644 Documentation/devicetree/bindings/rtc/dallas,ds1339.txt > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/i2c/trivial-devices.txt b/Documentation/devicetree/bindings/i2c/trivial-devices.txt > > > > > > index 6af570e..e9206a4 100644 > > > > > > --- a/Documentation/devicetree/bindings/i2c/trivial-devices.txt > > > > > > +++ b/Documentation/devicetree/bindings/i2c/trivial-devices.txt > > > > > > @@ -35,7 +35,6 @@ catalyst,24c32 i2c serial eeprom > > > > > > cirrus,cs42l51 Cirrus Logic CS42L51 audio codec > > > > > > dallas,ds1307 64 x 8, Serial, I2C Real-Time Clock > > > > > > dallas,ds1338 I2C RTC with 56-Byte NV RAM > > > > > > -dallas,ds1339 I2C Serial Real-Time Clock > > > > > > dallas,ds1340 I2C RTC with Trickle Charger > > > > > > dallas,ds1374 I2C, 32-Bit Binary Counter Watchdog RTC with Trickle Charger and Reset Input/Output > > > > > > dallas,ds1631 High-Precision Digital Thermometer > > > > > > diff --git a/Documentation/devicetree/bindings/rtc/dallas,ds1339.txt b/Documentation/devicetree/bindings/rtc/dallas,ds1339.txt > > > > > > new file mode 100644 > > > > > > index 0000000..9faf40e > > > > > > --- /dev/null > > > > > > +++ b/Documentation/devicetree/bindings/rtc/dallas,ds1339.txt > > > > > > @@ -0,0 +1,19 @@ > > > > > > +* Dallas DS1339 I2C Serial Real-Time Clock > > > > > > + > > > > > > +Required properties: > > > > > > +- compatible: Should contain "dallas,ds1339". > > > > > > +- reg: I2C address for chip > > > > > > + > > > > > > +Optional properties: > > > > > > +- trickle_setup : Used Trickle Charger configuration, > > > > > > + corresponding to 5 lowest bits in trickle charger register. > > > > > > > > > The value is provided via platform data, so it is platform specific > > > > and presumably needs to be configurable. I did, however, not find > > > > a single in-kernel driver which is actually setting it. > > > > So this is a good question. > > > > > > I'm uncomfortable adding a field we don't understand to DT. > > > > > > Is there any publicly-available documentation for the device? > > > > > > > Lots ;-) > > > > http://datasheets.maximintegrated.com/en/ds/DS1307.pdf > > http://datasheets.maximintegrated.com/en/ds/DS1337.pdf > > http://datasheets.maximintegrated.com/en/ds/DS1338.pdf > > http://datasheets.maximintegrated.com/en/ds/DS1339.pdf > > http://datasheets.maximintegrated.com/en/ds/DS1340.pdf > > http://datasheets.maximintegrated.com/en/ds/DS1388.pdf > > http://datasheets.maximintegrated.com/en/ds/DS3231.pdf > > > > Code suggests that DS1339, DS1339, and DS1340 have the register. > > > > Looking into the datasheets, the configuration consists of two parts: > > - diode connected or not > > - trickle charger resistor value (250, 2000, or 4000 ohm) > > > > Given that, it seems to me that those values should be configured > > explicitly instead of using a binary value, and that the driver > > should perform the conversion from dt entry to register value. > > iiuc, there is no way for the kernel to determine what is being trickle > charged, and thus no way to determine how it should set this register. > > It may be a bit of overkill, but I think a DT macro would be the most > maintainable solution here: > > #define DS1339_TRCKL_DIODE 0x08 > #define DS1339_TRCKL_NODIODE 0x04 > #define DS1339_TRCKL_R250 0x01 > #define DS1339_TRCKL_R2000 0x02 > #define DS1339_TRCKL_R4000 0x03 > > trickle_setup = <DS1339_TRCKL_DIODE | DS1339_TRCKL_R250>; > > And the driver would take care of oring it with the enable pattern. > Yes, that sounds reasonable as well. 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