From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Thompson Subject: Re: [PATCH 0/4] Add a generic driver for LED-based backlight Date: Fri, 5 Jul 2019 11:29:59 +0100 Message-ID: <20190705102959.cmqhzpzikqjsydlx@holly.lan> References: <20190701151423.30768-1-jjhiblot@ti.com> <20190705101434.fw5rpctnqt6dwg6e@devuan> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <20190705101434.fw5rpctnqt6dwg6e@devuan> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Pavel Machek Cc: mark.rutland@arm.com, jingoohan1@gmail.com, tomi.valkeinen@ti.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, robh+dt@kernel.org, jacek.anaszewski@gmail.com, Jean-Jacques Hiblot , lee.jones@linaro.org, linux-leds@vger.kernel.org, dmurphy@ti.com List-Id: linux-leds@vger.kernel.org T24gRnJpLCBKdWwgMDUsIDIwMTkgYXQgMTI6MTQ6MzRQTSArMDIwMCwgUGF2ZWwgTWFjaGVrIHdy b3RlOgo+IE9uIE1vbiAyMDE5LTA3LTAxIDE3OjE0OjE5LCBKZWFuLUphY3F1ZXMgSGlibG90IHdy b3RlOgo+ID4gVGhpcyBzZXJpZXMgYWltcyB0byBhZGQgYSBsZWQtYmFja2xpZ2h0IGRyaXZlciwg c2ltaWxhciB0byBwd20tYmFja2xpZ2h0LAo+ID4gYnV0IHVzaW5nIGEgTEVEIGNsYXNzIGRldmlj ZSB1bmRlcm5lYXRoLgo+ID4gCj4gPiBBIGZldyB5ZWFycyBhZ28gKDIwMTUpLCBUb21pIFZhbGtl aW5lbiBwb3N0ZWQgYSBzZXJpZXMgaW1wbGVtZW50aW5nIGEKPiA+IGJhY2tsaWdodCBkcml2ZXIg b24gdG9wIG9mIGEgTEVEIGRldmljZToKPiA+IGh0dHBzOi8vcGF0Y2h3b3JrLmtlcm5lbC5vcmcv cGF0Y2gvNzI5Mzk5MS8KPiA+IGh0dHBzOi8vcGF0Y2h3b3JrLmtlcm5lbC5vcmcvcGF0Y2gvNzI5 NDAwMS8KPiA+IGh0dHBzOi8vcGF0Y2h3b3JrLmtlcm5lbC5vcmcvcGF0Y2gvNzI5Mzk4MS8KPiA+ IAo+ID4gVGhlIGRpc2N1c3Npb24gc3RvcHBlZCBiZWNhdXNlIFRvbWkgbGFja2VkIHRoZSB0aW1l IHRvIHdvcmsgb24gaXQuCj4gPiAKPiA+IFRoaXMgc2VyaWVzIHRha2VzIGl0IGZyb20gdGhlcmUg YW5kIGltcGxlbWVudHMgdGhlIGJpbmRpbmcgdGhhdCB3YXMKPiA+IGRpc2N1c3NlZCBpbiBodHRw czovL3BhdGNod29yay5rZXJuZWwub3JnL3BhdGNoLzcyOTM5OTEvLiBJbiB0aGlzIG5ldwo+ID4g YmluZGluZyB0aGUgYmFja2xpZ2h0IGRldmljZSBpcyBhIGNoaWxkIG9mIHRoZSBMRUQgY29udHJv bGxlciBpbnN0ZWFkIG9mCj4gPiBiZWluZyBhbm90aGVyIHBsYXRmb3JtIGRldmljZSB0aGF0IHVz ZXMgYSBwaGFuZGxlIHRvIHJlZmVyZW5jZSBhIExFRC4KPiAKPiBPdGhlciBvcHRpb24gd291bGQg YmUgdG8gaGF2ZSBiYWNrbGlnaHQgdHJpZ2dlci4gV2hhdCBhcmUKPiBhZHZhbnRhZ2VzL2Rpc2Fk dmFudGFnZXMgcmVsYXRpdmUgdG8gdGhhdD8KCkkgc3BlbnQgYSBsaXR0bGUgdGltZSB0aGlua2lu ZyBhYm91dCB0aGF0IGR1cmluZyB0aGUgcmVjZW50IHJvdW5kIG9mCnJldmlld3MuCgpNeSByb3Vn aCB0aG91Z2h0cyB3ZXJlIHRoYXQgTEVEIHRyaWdnZXJzIHdvdWxkIGJlIGEgZ29vZCB3YXkgdG8K aGFuZGxlIGl0IGluIHRoZSBrZXJuZWwgY29kZSBhbmQgd291bGQgdHJpdmlhbGx5IHNvbHZlIGEg YmFja2xpZ2h0CmNvbXBvc2VkIG9mIG11bHRpcGxlIExFRCBkZXZpY2VzIChzaW5jZSBhbGwgY291 bGQgYXR0YWNoIHRvIHRoZSBzYW1lCnRyaWdnZXIpLiBIb3dldmVyIEkgdGhpbmsgaXQgd291bGQg YmUgZGlmZmljdWx0IHRvIHVzZSB0aGUgZXhpc3RpbmcgRFQKYmluZGluZ3MgZm9yIHRyaWdnZXJz IHRvIGV4cHJlc3MgdGhpbmdzIGxpa2UgYnJpZ2h0bmVzcyBjdXJ2ZXMgYW5kIHRvCmhhbmRsZSBz eXN0ZW1zIHdpdGggbXVsdGlwbGUgaGVhZHMuCgpJJ20gbm90ICp0b28qIHdvcnJpZWQgYWJvdXQg Y29uZmxpY3Qgd2l0aCB0aGUgZXhpc3RpbmcgYmFja2xpZ2h0IHRyaWdnZXIKKHdoaWNoIGlzbid0 IGFjdHVhbGx5IGEgYmFja2xpZ2h0Li4uIGp1c3QgYSBob29rIGludG8gdGhlIGZyYW1lYnVmZmVy CmNvZGUgdG8gb3BlcmF0ZSBhIGJpbmFyeSBMRUQpLiBQZW9wbGUgbGlrZSBEYW5pZWwgVmV0dGVy IGFyZQpsYWJvdXJpbmcgZGlsaWdlbnRseSB0byBnZXQgcmlkIG9mIHRoZSBub3RpZmllciBpdCBk ZXBlbmRzIG9uIHNvIHR1cm5pbmcKaXQgaW50byBhIHByb3BlciBiYWNrbGlnaHQgZGV2aWNlIHdv dWxkIHByb2JhYmx5IGhlbHAgd2l0aCB0aGF0IGVmZm9ydC4KCkFueWhvdy4uLiBoYXZpbmcgdGhv dWdodCB0aGUgYWJvdmUgSSB0aGVuIHNob29rIG15c2VsZiBhIGJpdCBhbmQKZmlndXJlZCBpdCB3 YXMgbW9yZSBpbXBvcnRhbnQgdG8gZm9jdXMgb24gc2FuZSBiaW5kaW5ncyB0aGF0IG9uIHdoYXQK dGhlIGtlcm5lbCBkb2VzIHVuZGVyIHRoZSBjb3ZlcnMgdG8gcmVhbGl6ZSB0aGVtIDstKSBhbmQg ZGVjaWRlZCB0byBrZWVwCnF1aWV0IHVudGlsIHRoZSBuZXh0IHNldCBvZiBiaW5kaW5ncyBpcyBw cm9wb3NlZC4KCkhvd2V2ZXIuLi4gc2luY2UgeW91IGFza2VkLi4uCgoKCkRhbmllbC4KX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KZHJpLWRldmVsIG1haWxp bmcgbGlzdApkcmktZGV2ZWxAbGlzdHMuZnJlZWRlc2t0b3Aub3JnCmh0dHBzOi8vbGlzdHMuZnJl ZWRlc2t0b3Aub3JnL21haWxtYW4vbGlzdGluZm8vZHJpLWRldmVs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BAD5EC46499 for ; 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[82.132.213.94]) by smtp.gmail.com with ESMTPSA id y10sm5524508wmj.2.2019.07.05.03.30.05 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 05 Jul 2019 03:30:07 -0700 (PDT) Date: Fri, 5 Jul 2019 11:29:59 +0100 From: Daniel Thompson To: Pavel Machek Cc: Jean-Jacques Hiblot , jacek.anaszewski@gmail.com, robh+dt@kernel.org, mark.rutland@arm.com, lee.jones@linaro.org, jingoohan1@gmail.com, dmurphy@ti.com, linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, tomi.valkeinen@ti.com Subject: Re: [PATCH 0/4] Add a generic driver for LED-based backlight Message-ID: <20190705102959.cmqhzpzikqjsydlx@holly.lan> References: <20190701151423.30768-1-jjhiblot@ti.com> <20190705101434.fw5rpctnqt6dwg6e@devuan> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline In-Reply-To: <20190705101434.fw5rpctnqt6dwg6e@devuan> User-Agent: NeoMutt/20180716 Sender: linux-leds-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-leds@vger.kernel.org Message-ID: <20190705102959.bgDFbKcWOlMggg1PoBJiLW0SHupmgftqd9ofRqjixmQ@z> On Fri, Jul 05, 2019 at 12:14:34PM +0200, Pavel Machek wrote: > On Mon 2019-07-01 17:14:19, Jean-Jacques Hiblot wrote: > > This series aims to add a led-backlight driver, similar to pwm-backlight, > > but using a LED class device underneath. > > > > A few years ago (2015), Tomi Valkeinen posted a series implementing a > > backlight driver on top of a LED device: > > https://patchwork.kernel.org/patch/7293991/ > > https://patchwork.kernel.org/patch/7294001/ > > https://patchwork.kernel.org/patch/7293981/ > > > > The discussion stopped because Tomi lacked the time to work on it. > > > > This series takes it from there and implements the binding that was > > discussed in https://patchwork.kernel.org/patch/7293991/. In this new > > binding the backlight device is a child of the LED controller instead of > > being another platform device that uses a phandle to reference a LED. > > Other option would be to have backlight trigger. What are > advantages/disadvantages relative to that? I spent a little time thinking about that during the recent round of reviews. My rough thoughts were that LED triggers would be a good way to handle it in the kernel code and would trivially solve a backlight composed of multiple LED devices (since all could attach to the same trigger). However I think it would be difficult to use the existing DT bindings for triggers to express things like brightness curves and to handle systems with multiple heads. I'm not *too* worried about conflict with the existing backlight trigger (which isn't actually a backlight... just a hook into the framebuffer code to operate a binary LED). People like Daniel Vetter are labouring diligently to get rid of the notifier it depends on so turning it into a proper backlight device would probably help with that effort. Anyhow... having thought the above I then shook myself a bit and figured it was more important to focus on sane bindings that on what the kernel does under the covers to realize them ;-) and decided to keep quiet until the next set of bindings is proposed. However... since you asked... Daniel.