linux-kernel - Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

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Date:   Tue, 17 Oct 2017 19:46:03 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Brian Norris <briannorris@...omium.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Heiko Stübner <heiko@...ech.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Doug Anderson <dianders@...omium.org>, tfiga@...omium.org,
        seanpaul@...omium.org,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

On Tue, Oct 17, 2017 at 11:24:24AM -0700, Dmitry Torokhov wrote:
> On Tue, Oct 17, 2017 at 10:04 AM, Brian Norris <briannorris@...omium.org> wrote:

> > BTW, since you seem to have an opinion about device links: is it
> > expected that all consumer drivers will make explicit calls to
> > device_link_add()? I thought this should be avoided, if possible (e.g.,
> > this can be handled in pwm_get()).

> Ideally we would not have this in core kernel API (pwm_get, gpiod_get,
> regulator_get, etc) but retrieve it form the firmware (device tree,
> ACPI) and use this data not only on suspend/resume but for probing as

Right, the major initial push here was for ordering of probes so doing
it in subsystems or drivers is too late.

> well. *How exactly* can we do that is still not clear though, so maybe
> we could plug the biggest holes by actually adding device links calls
> to the main devm_<object>_get() users...

I would expect we can get a long way in the DT by doing a pass over the
tree and adding links between device nodes in cases where phandle
references exist.  There is a potential issue with circular links which
I'm just going to handwave away right now but I'd expect that to help
otherwise.

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