From: nicolas.ferre@atmel•com (Nicolas Ferre)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC 4/5] RTC: rtc-at91sam9: add device-tree support
Date: Mon, 8 Apr 2013 11:57:06 +0200 [thread overview]
Message-ID: <51629472.3070404@atmel.com> (raw)
In-Reply-To: <20130408090023.GC25605@localhost>
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 <jhovold@gmail•com>
>>> ---
>>> .../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 at 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
next prev parent reply other threads:[~2013-04-08 9:57 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-04 3:54 [PATCH] rtc: rtc-at91sam9.c add DT support Douglas Gilbert
2013-04-04 8:11 ` Nicolas Ferre
2013-04-04 13:25 ` Douglas Gilbert
2013-04-04 14:08 ` Nicolas Ferre
2013-04-04 19:14 ` Douglas Gilbert
2013-04-07 15:09 ` Johan Hovold
[not found] ` <1365347572-14972-1-git-send-email-jhovold@gmail.com>
2013-04-08 7:33 ` [RFC 1/5] ARM: at91: add general purpose backup register (GPBR) support Jean-Christophe PLAGNIOL-VILLARD
2013-04-08 8:46 ` Johan Hovold
2013-04-08 10:04 ` Jean-Christophe PLAGNIOL-VILLARD
2013-04-11 12:39 ` Johan Hovold
2013-04-11 14:53 ` Jean-Christophe PLAGNIOL-VILLARD
[not found] ` <1365347572-14972-2-git-send-email-jhovold@gmail.com>
2013-04-08 7:35 ` [RFC 2/5] ARM: at91/dts: " Jean-Christophe PLAGNIOL-VILLARD
[not found] ` <1365347572-14972-4-git-send-email-jhovold@gmail.com>
2013-04-08 7:38 ` [RFC 4/5] RTC: rtc-at91sam9: add device-tree support Jean-Christophe PLAGNIOL-VILLARD
2013-04-08 9:00 ` Johan Hovold
2013-04-08 9:57 ` Nicolas Ferre [this message]
2013-04-08 10:03 ` Jean-Christophe PLAGNIOL-VILLARD
2013-04-08 10:42 ` Nicolas Ferre
2013-04-08 11:02 ` Jean-Christophe PLAGNIOL-VILLARD
2013-04-08 10:48 ` Johan Hovold
2013-04-08 11:08 ` Jean-Christophe PLAGNIOL-VILLARD
2013-04-08 10:38 ` Johan Hovold
2013-04-08 11:11 ` Jean-Christophe PLAGNIOL-VILLARD
2013-04-11 12:57 ` Johan Hovold
2013-04-04 8:16 ` [PATCH] rtc: rtc-at91sam9.c add DT support Johan Hovold
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