From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Date: Thu, 13 Jun 2019 15:43:57 +0000 Subject: Re: [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels Message-Id: <20190613154357.GN137143@google.com> List-Id: References: <20190612180003.161966-1-mka@chromium.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Enric Balletbo i Serra Cc: linux-pwm@vger.kernel.org, Daniel Thompson , Douglas Anderson , Bartlomiej Zolnierkiewicz , Jingoo Han , Brian Norris , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Thierry Reding , Jacek Anaszewski , Pavel Machek , Lee Jones On Thu, Jun 13, 2019 at 11:14:55AM +0200, Enric Balletbo i Serra wrote: > Hi Matthias, > > On 12/6/19 20:00, Matthias Kaehlcke wrote: > > With commit 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of > > LED linearly to human eye") the number of set bits (aka hweight()) > > in the PWM period is used in the heuristic to determine the number > > of brightness levels, when the brightness table isn't specified in > > the DT. The number of set bits doesn't provide a reliable clue about > > the length of the period, instead change the heuristic to: > > > > nlevels = period / fls(period) > > > > Also limit the maximum number of brightness levels to 4096 to avoid > > excessively large tables. > > > > With this the number of levels increases monotonically with the PWM > > period, until the maximum of 4096 levels is reached: > > > > period (ns) # levels > > > > 100 16 > > 500 62 > > 1000 111 > > 5000 416 > > 10000 769 > > 50000 3333 > > 100000 4096 > > > > Fixes: 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye") > > Signed-off-by: Matthias Kaehlcke > > Tested on Samsung Chromebook Plus (16-bit pwm) > > Tested-by: Enric Balletbo i Serra Thanks! From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels Date: Thu, 13 Jun 2019 08:43:57 -0700 Message-ID: <20190613154357.GN137143@google.com> References: <20190612180003.161966-1-mka@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Enric Balletbo i Serra Cc: linux-pwm@vger.kernel.org, Daniel Thompson , Douglas Anderson , Bartlomiej Zolnierkiewicz , Jingoo Han , Brian Norris , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Thierry Reding , Jacek Anaszewski , Pavel Machek , Lee Jones List-Id: linux-pwm@vger.kernel.org T24gVGh1LCBKdW4gMTMsIDIwMTkgYXQgMTE6MTQ6NTVBTSArMDIwMCwgRW5yaWMgQmFsbGV0Ym8g aSBTZXJyYSB3cm90ZToKPiBIaSBNYXR0aGlhcywKPiAKPiBPbiAxMi82LzE5IDIwOjAwLCBNYXR0 aGlhcyBLYWVobGNrZSB3cm90ZToKPiA+IFdpdGggY29tbWl0IDg4YmE5NWJlZGI3OSAoImJhY2ts aWdodDogcHdtX2JsOiBDb21wdXRlIGJyaWdodG5lc3Mgb2YKPiA+IExFRCBsaW5lYXJseSB0byBo dW1hbiBleWUiKSB0aGUgbnVtYmVyIG9mIHNldCBiaXRzIChha2EgaHdlaWdodCgpKQo+ID4gaW4g dGhlIFBXTSBwZXJpb2QgaXMgdXNlZCBpbiB0aGUgaGV1cmlzdGljIHRvIGRldGVybWluZSB0aGUg bnVtYmVyCj4gPiBvZiBicmlnaHRuZXNzIGxldmVscywgd2hlbiB0aGUgYnJpZ2h0bmVzcyB0YWJs ZSBpc24ndCBzcGVjaWZpZWQgaW4KPiA+IHRoZSBEVC4gVGhlIG51bWJlciBvZiBzZXQgYml0cyBk b2Vzbid0IHByb3ZpZGUgYSByZWxpYWJsZSBjbHVlIGFib3V0Cj4gPiB0aGUgbGVuZ3RoIG9mIHRo ZSBwZXJpb2QsIGluc3RlYWQgY2hhbmdlIHRoZSBoZXVyaXN0aWMgdG86Cj4gPiAKPiA+ICBubGV2 ZWxzID0gcGVyaW9kIC8gZmxzKHBlcmlvZCkKPiA+IAo+ID4gQWxzbyBsaW1pdCB0aGUgbWF4aW11 bSBudW1iZXIgb2YgYnJpZ2h0bmVzcyBsZXZlbHMgdG8gNDA5NiB0byBhdm9pZAo+ID4gZXhjZXNz aXZlbHkgbGFyZ2UgdGFibGVzLgo+ID4gCj4gPiBXaXRoIHRoaXMgdGhlIG51bWJlciBvZiBsZXZl bHMgaW5jcmVhc2VzIG1vbm90b25pY2FsbHkgd2l0aCB0aGUgUFdNCj4gPiBwZXJpb2QsIHVudGls IHRoZSBtYXhpbXVtIG9mIDQwOTYgbGV2ZWxzIGlzIHJlYWNoZWQ6Cj4gPiAKPiA+IHBlcmlvZCAo bnMpICAgICMgbGV2ZWxzCj4gPiAKPiA+IDEwMCAgICAJICAgICAgIDE2Cj4gPiA1MDAJICAgICAg IDYyCj4gPiAxMDAwCSAgICAgICAxMTEKPiA+IDUwMDAJICAgICAgIDQxNgo+ID4gMTAwMDAJICAg ICAgIDc2OQo+ID4gNTAwMDAJICAgICAgIDMzMzMKPiA+IDEwMDAwMAkgICAgICAgNDA5Ngo+ID4g Cj4gPiBGaXhlczogODhiYTk1YmVkYjc5ICgiYmFja2xpZ2h0OiBwd21fYmw6IENvbXB1dGUgYnJp Z2h0bmVzcyBvZiBMRUQgbGluZWFybHkgdG8gaHVtYW4gZXllIikKPiA+IFNpZ25lZC1vZmYtYnk6 IE1hdHRoaWFzIEthZWhsY2tlIDxta2FAY2hyb21pdW0ub3JnPgo+IAo+IFRlc3RlZCBvbiBTYW1z dW5nIENocm9tZWJvb2sgUGx1cyAoMTYtYml0IHB3bSkKPiAKPiBUZXN0ZWQtYnk6IEVucmljIEJh bGxldGJvIGkgU2VycmEgPGVucmljLmJhbGxldGJvQGNvbGxhYm9yYS5jb20+CgpUaGFua3MhCl9f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmRyaS1kZXZlbCBt YWlsaW5nIGxpc3QKZHJpLWRldmVsQGxpc3RzLmZyZWVkZXNrdG9wLm9yZwpodHRwczovL2xpc3Rz LmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2RyaS1kZXZlbA== 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=-5.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 59E0EC31E45 for ; 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Thu, 13 Jun 2019 08:44:00 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id w66sm83713pfb.47.2019.06.13.08.43.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 08:43:59 -0700 (PDT) Date: Thu, 13 Jun 2019 08:43:57 -0700 From: Matthias Kaehlcke To: Enric Balletbo i Serra Cc: Thierry Reding , Lee Jones , Daniel Thompson , Jingoo Han , Bartlomiej Zolnierkiewicz , linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Douglas Anderson , Brian Norris , Pavel Machek , Jacek Anaszewski Subject: Re: [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels Message-ID: <20190613154357.GN137143@google.com> References: <20190612180003.161966-1-mka@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 13, 2019 at 11:14:55AM +0200, Enric Balletbo i Serra wrote: > Hi Matthias, > > On 12/6/19 20:00, Matthias Kaehlcke wrote: > > With commit 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of > > LED linearly to human eye") the number of set bits (aka hweight()) > > in the PWM period is used in the heuristic to determine the number > > of brightness levels, when the brightness table isn't specified in > > the DT. The number of set bits doesn't provide a reliable clue about > > the length of the period, instead change the heuristic to: > > > > nlevels = period / fls(period) > > > > Also limit the maximum number of brightness levels to 4096 to avoid > > excessively large tables. > > > > With this the number of levels increases monotonically with the PWM > > period, until the maximum of 4096 levels is reached: > > > > period (ns) # levels > > > > 100 16 > > 500 62 > > 1000 111 > > 5000 416 > > 10000 769 > > 50000 3333 > > 100000 4096 > > > > Fixes: 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye") > > Signed-off-by: Matthias Kaehlcke > > Tested on Samsung Chromebook Plus (16-bit pwm) > > Tested-by: Enric Balletbo i Serra Thanks!