From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757185Ab1LGSFJ (ORCPT ); Wed, 7 Dec 2011 13:05:09 -0500 Received: from mail-ee0-f46.google.com ([74.125.83.46]:49845 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756788Ab1LGSFH (ORCPT ); Wed, 7 Dec 2011 13:05:07 -0500 Message-ID: <4EDFAA0A.7040607@solonet.org.ua> Date: Wed, 07 Dec 2011 20:01:46 +0200 From: Denis Kuzmenko User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20111110 Icedove/3.0.11 MIME-Version: 1.0 To: Linus Walleij CC: Linus Walleij , Richard Purdie , linux-kernel@vger.kernel.org, Andrew Morton , Samuel Ortiz , Shreshtha Kumar Sahu Subject: Re: [PATCH] leds: driver for ab5500 high voltage leds References: <1322834182-26168-1-git-send-email-linus.walleij@stericsson.com> <4EDAA785.40503@solonet.org.ua> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/07/2011 04:07 PM, Linus Walleij wrote: > On Sat, Dec 3, 2011 at 11:49 PM, Denis Kuzmenko wrote: > >> (snip) >>> diff --git a/drivers/leds/leds-ab5500.c b/drivers/leds/leds-ab5500.c >> (snip) >>> +/* >>> + * Driver for HVLED in ST-Ericsson AB5500 analog baseband controller >>> + * >>> + * This chip can drive upto 3 leds, of upto 40mA of led sink current. >> >> Can't get these are High Voltage or High Current LEDs? >> If Voltage why haven't you wrote about supplied voltage but wrote about >> max. current? > > The three channels are indeed high-voltage LEDs, they supply > up to 20V from a supply voltage of some standard mobile handset > battery at say 3.8 V or so. But there is no register to control the > voltage or anything like that. > > My naive understanding is that you set the current limit and then > the HV transformer (I guess this is a buck converter of some kind) > will raise the voltage level until it either (A) cannot raise it any more > at c:a 20V or (b) the current limit is reached. > > I suspect this is because for LEDs of this type you get a > specified current but the voltage just has to be "high enough" > to break through some diode barrier threshold or so. After > that intensity is controlled by limiting the current. > > Does this suffice as explanation...? > > Yours, > Linus Walleij Yeah, It does, thank you. Does it worth to make additional comment in code to avoid further questions? -- Best regards, Denis Kuzmenko.