Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 10 Sep 2019 21:06:48 +0200
From:   Andreas Kemnade <andreas@kemnade.info>
To:     Daniel Thompson <daniel.thompson@linaro.org>
Cc:     lee.jones@linaro.org, jingoohan1@gmail.com,
        jacek.anaszewski@gmail.com, pavel@ucw.cz, dmurphy@ti.com,
        robh+dt@kernel.org, mark.rutland@arm.com, b.zolnierkie@samsung.com,
        dri-devel@lists.freedesktop.org, linux-leds@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fbdev@vger.kernel.org,
        "H. Nikolaus Schaller" <hns@goldelico.com>
Subject: Re: [PATCH 1/2] backlight: lm3630a: add an enable gpio for the HWEN
 pin
Message-ID: <20190910210648.3594912d@kemnade.info>
In-Reply-To: <20190910102156.vmprsjebmlphkv34@holly.lan>
References: <20190908203704.30147-1-andreas@kemnade.info>
        <20190908203704.30147-2-andreas@kemnade.info>
        <20190909105729.w5552rtop7rhghy2@holly.lan>
        <20190909221349.46ca5a1f@aktux>
        <20190910102156.vmprsjebmlphkv34@holly.lan>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
 boundary="Sig_/d51yUFk84RybqHzz4cluJyL"; protocol="application/pgp-signature"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

--Sig_/d51yUFk84RybqHzz4cluJyL
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable

On Tue, 10 Sep 2019 11:21:56 +0100
Daniel Thompson <daniel.thompson@linaro.org> wrote:

[...]
> > > Is this needed?
> > >=20
> > > This is a remove path, not a power management path, and we have no id=
ea
> > > what the original status of the pin was anyway?
> > >  =20
> >=20
> > Looking at Ishdn on page 5 of the datasheet, switching it off everytime
> > possible seems not needed. We would need to call chip_init() everytime
> > we enable the gpio or live with default values.
> > Therefore I did decide to not put it into any power management path.
> > But switching it on and not switching it off feels so unbalanced.  =20
>=20
> Either the power consumed by the controller when strings aren't lit up
> matters, in which case the driver should implement proper power
> management or it doesn't matter and changing the pin state isn't needed.
>=20
> I'm happy with either of the above but this looks like a third way,
> where eager users could hack in a bit of extra power management by
> forcing drivers to unbind.=20
>=20
I think I will take the simple way. I am quite sure that the power
consumption with HWEN on and leds off does not matter. If someone
later comes up and finds out that I misread the datasheet, things
are prepared to be improved.
At least the hardware can be properly described in the devicetree.

Regards,
Andreas

--Sig_/d51yUFk84RybqHzz4cluJyL
Content-Type: application/pgp-signature
Content-Description: OpenPGP digital signature

-----BEGIN PGP SIGNATURE-----
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=SLZS
-----END PGP SIGNATURE-----

--Sig_/d51yUFk84RybqHzz4cluJyL--