From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicolas Ferre Subject: Re: [RFC 4/5] RTC: rtc-at91sam9: add device-tree support Date: Mon, 8 Apr 2013 11:57:06 +0200 Message-ID: <51629472.3070404@atmel.com> References: <20130407150938.GA25605@localhost> <1365347572-14972-1-git-send-email-jhovold@gmail.com> <1365347572-14972-4-git-send-email-jhovold@gmail.com> <20130408073807.GQ20693@game.jcrosoft.org> <20130408090023.GC25605@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130408090023.GC25605@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Johan Hovold Cc: devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Robert Nelson , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, dgilbert-qazKcTl6WRFWk0Htik3J/w@public.gmane.org List-Id: devicetree@vger.kernel.org On 04/08/2013 11:00 AM, Johan Hovold : > On Mon, Apr 08, 2013 at 09:38:07AM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote: >> On 17:12 Sun 07 Apr , Johan Hovold wrote: >>> Add device-tree support. >>> >>> The AT91 RTT can be used as an RTC if the atmel,at91-rtt-as-rtc-gpbr >>> property is present and set to the general-purpose backup register to >>> use to store the RTC time base. >>> >>> Signed-off-by: Johan Hovold >>> --- >>> .../devicetree/bindings/rtc/rtc-at91sam9.txt | 19 ++++++++++++ >>> drivers/rtc/rtc-at91sam9.c | 36 +++++++++++++++++++++- >>> 2 files changed, 54 insertions(+), 1 deletion(-) >>> create mode 100644 Documentation/devicetree/bindings/rtc/rtc-at91sam9.txt >>> >>> diff --git a/Documentation/devicetree/bindings/rtc/rtc-at91sam9.txt b/Documentation/devicetree/bindings/rtc/rtc-at91sam9.txt >>> new file mode 100644 >>> index 0000000..0f54988 >>> --- /dev/null >>> +++ b/Documentation/devicetree/bindings/rtc/rtc-at91sam9.txt >>> @@ -0,0 +1,19 @@ >>> +Atmel AT91 RTT as RTC >>> +===================== >>> + >>> +Required properties: >>> +- compatible: Should be "atmel,at91sam9260-rtt" >>> +- reg: Should contain register location and length >>> +- interrupts: Should contain interrupt for the RTT which is the IRQ line >>> + shared across all System Controller members. >>> +- atmel,rtt-as-rtc-gpbr: Should contain the backup-register to use to store >>> + the RTC time base >>> + >>> +Example: >>> + >>> +rtt@fffffd20 { >>> + compatible = "atmel,at91sam9g45-rtt", "atmel,at91sam9260-rtt"; No, there is no visible difference between the sam9g45 RTT and the sam9260 one. So the most precise compatibility string is still sam9260. If one day we feel the need for a advanced feature that exists on a more recent SoC, we have the possibility to add it at that time... >>> + reg = <0xfffffd20 0x10>; >>> + interrupts = <1 4 7>; >>> + atmel,at91-rtt-as-rtc-gpbr = <0>; >> no you miss the point of the DT >> >> you need to describe the hardware no a particular use of it > > That was what I was trying to achieve by adding the two use-neutral > rtt and gpbr-nodes. But then the question is how would you influence > which out of two rtt-drivers to use? > > Adding a property as above in the final board descriptions seemed > preferable to adding rtt-as-rtc to the compatible string of the rtt as > that would mean describing use rather than just hardware. Well, re-reading the Device_Tree_Usage page, I found this sentence: " Understanding the compatible Property Every node in the tree that represents a device is required to have the compatible property. compatible is the key an operating system uses to decide which device driver to bind to a device. " or ePARP: " The compatible property value consists of one or more strings that define the specific programming model for the device. " We have the notion of link between hardware and software in this *compatible* sting, even if the *node* itself is about hardware description. >> the RTT is a general purpose timer backuped that we use in linux as a >> RTC with a gpbr to store the time >> >> you need 2 binding on for the RTT one the RTT-rtc > > As in adding some virtual hardware-node which uses the rtt and gpbr as > resources? So, why not simply having a compatibility string that collects the uses of this RTT node: compatible = "atmel,at91sam9260-rtt-as-rtc", "atmel,at91sam9260-rtt"; And then "decide which device driver to bind to [the RTT] device"... If the rtt-as-rtc driver is not selected, the device can still be used as a simple "rtt". The board .dts can overload a compatibility string according to the use, etc. Then the way do describe which GPBR to use has still to be discussed. But for the RTT itself, I would keep it simple like that. Best regards, -- Nicolas Ferre