linux-kernel - Re: [PATCH v2 2/2] of: changesets: Introduce changeset helper methods

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Date:	Mon, 21 Sep 2015 15:07:08 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Cc:	Rob Herring <robherring2@...il.com>,
	Frank Rowand <frowand.list@...il.com>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] of: changesets: Introduce changeset helper methods

Hi Pantelis,

On Mon, Sep 21, 2015 at 2:49 PM, Pantelis Antoniou
<pantelis.antoniou@...sulko.com> wrote:
>> On Sep 21, 2015, at 15:47 , Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> On Mon, Sep 21, 2015 at 2:36 PM, Pantelis Antoniou
>> <pantelis.antoniou@...sulko.com> wrote:
>>>> On Sep 21, 2015, at 15:35 , Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>>> On Wed, Sep 16, 2015 at 6:11 PM, Pantelis Antoniou
>>>> <pantelis.antoniou@...sulko.com> wrote:
>>>>> Changesets are very powerful, but the lack of a helper API
>>>>> makes using them cumbersome. Introduce a simple copy based
>>>>> API that makes things considerably easier.
>>>>>
>>>>> To wit, adding a property using the raw API.
>>>>>
>>>>>       struct property *prop;
>>>>>       prop = kzalloc(sizeof(*prop)), GFP_KERNEL);
>>>>>       prop->name = kstrdup("compatible");
>>>>>       prop->value = kstrdup("foo,bar");
>>>>>       prop->length = strlen(prop->value) + 1;
>>>>>       of_changeset_add_property(ocs, np, prop);
>>>>>
>>>>> while using the helper API
>>>>>
>>>>>       of_changeset_add_property_string(ocs, np, "compatible",
>>>>>                       "foo,bar");
>>>>
>>>> What about removing properties?
>>>
>>> Once upon a time there was that capability. It was removed after we didn’t have
>>> a good use for them yet. Do you have any? I’d be happy to re-add it :)
>>
>> Aliases?
>>
>> If an overlay removes e.g. a serial port, it should remove its alias, too.
>
> Well, that case is handled. Addition of a property results in removal of a property when
> the overlay is reverted.

Actually what I meant is the other way around: _adding_ the overlay would
_remove_ the alias.

I have a board with an SDHI connector, and an expansion connector.
SDHI and serial on the expansion connector share the same pins.
By default, SDHI is enabled in the DTS.

To add a serial port to the expansion connector, I disable the SDHI device,
add the alias, and add the serial device.
(dtsi in http://www.spinics.net/lists/devicetree/msg79438.html)

Now imagine doing the opposite: having the serial device enabled by default.
Then the overlay should disable the serial device, remove the alias, and add
the SDHI device.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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