From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Kemnade Subject: Re: [PATCH 1/2] backlight: lm3630a: add an enable gpio for the HWEN pin Date: Tue, 10 Sep 2019 21:06:48 +0200 Message-ID: <20190910210648.3594912d@kemnade.info> 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" Return-path: In-Reply-To: <20190910102156.vmprsjebmlphkv34@holly.lan> Sender: linux-kernel-owner@vger.kernel.org To: Daniel Thompson 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" List-Id: devicetree@vger.kernel.org --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 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----- iQIzBAEBCAAdFiEEPIWxmAFyOaBcwCpFl4jFM1s/ye8FAl139EoACgkQl4jFM1s/ ye+ZZA//WKkB+xioM4V6ShKpqapJ3LzkVD0RhoEhoiY/5NgLwkF1m/w/6Z0LmHB/ 8nvWJXJpxmTtIUzFqn265zYZWJwsYCV5EmlEHKy/Bv/XKENCeqGubixw4POqkbgw APKbSabSXoGtlhuhQjFXOc6FbBBB5ynt6f7nliuY9xYbN+rUTBWEgRrdJ4ktdQn8 4sGtQv7jy41ogrZho1aUgpe7HAfuixlEUJlW9v2/i3a2n25uWCKMAt49nTns0xXv r4psgXQZs9pommPsaR799afcnFnWoHP7qW7kKsm9rSI5tq4hvJjEwbYCagpA9Rf8 fXOn2PIGMAg0L2Grxmggp6HC5qaKMnntUBiIj26yljvce0F8bH4xyb5rRTrOEasP PSR1Y/FxzC6AyD8ZbeEIZEjqRcpz7Y5+c5cnrgROBpfxHv3rjOXYR9bZkkKQ7unV HnHdPFHESb/p0jvj2cOFyoUFQkeTtbpIfeCoX11T2rPBmIq1RJUD6UsLTe2DRlC6 ex4vqW3RvQqTv5XIcUezPHUMVvmlUMyrx0XQyAVUGcnGYwxVBSLm1hMElaivuAM8 gzbfNAwuTgl1xNseaGH7nu/UoUAKk4vEYEncT4YHWLoFJ9HjlyKmZNuM/4j1z+sd R2t/co/S1lpJCYvEOChmcwtxSa8pVn14iysG+32Pk++AX7CoqCM= =SLZS -----END PGP SIGNATURE----- --Sig_/d51yUFk84RybqHzz4cluJyL--