linux-kernel - Re: [PATCH v6 04/22] of: add function to allow probing a device from a OF node

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Date:	Tue, 27 Oct 2015 15:46:07 +0100
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Rob Herring <robh+dt@...nel.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v6 04/22] of: add function to allow probing a device from
 a OF node

On 26 October 2015 at 09:16, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Mon, Sep 21, 2015 at 4:02 PM, Tomeu Vizoso
> <tomeu.vizoso@...labora.com> wrote:
>> Walks the OF tree up and finds the closest ancestor that has a struct
>> device associated with it, probing it if isn't bound to a driver yet.
>>
>> The above should ensure that the dependency represented by the passed OF
>> node is available, because probing a device should cause its descendants
>> to be probed as well (when they get registered).
>>
>> Subsystems can use this when looking up resources for drivers, to reduce
>> the chances of deferred probes because of the probing order of devices.
>>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>
> Don't know to which response I should post this comment, so I'm responding
> to the original email.
>
> Some subsystems already do this.
> If you call e.g. syscon_regmap_lookup_by_phandle(), it will call
> of_syscon_register() if the syscon device pointed to hasn't been registered yet.

Hi Geert,

I think I prefer if devices are registered as early as possible and
then only probed on-demand, as registration is very much
device-specific but probing is the same for all devices.

But I think in general we should be doing more things on demand and
depending less on the order in which we mass initialize stuff
(devices, classes, drivers, etc).

Regards,

Tomeu

> 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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