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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 C42DFC48BC2 for ; Wed, 23 Jun 2021 06:15:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A5CDC6101D for ; Wed, 23 Jun 2021 06:15:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229812AbhFWGSD (ORCPT ); Wed, 23 Jun 2021 02:18:03 -0400 Received: from so254-9.mailgun.net ([198.61.254.9]:52401 "EHLO so254-9.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229800AbhFWGSD (ORCPT ); Wed, 23 Jun 2021 02:18:03 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1624428946; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=YgXZ6VNhDITS6yDaGx56LtlJqbhq7xTELt1tz8y6TYM=; b=L8uDHvsVTSBBO5yxeEk2FcNdxCQlLcuHSd3uMhIj2Y2xiLXMtfTpCm6NG8skjaO1NO2QHJfh Usq7EyZZjqQAqW7vlhjNSAlrgmRvuwho/ixnxQDz+64ctRYnAYKx6tlF9VG1xRiKtNEM84px BUj0+0w2DphVh8qSX3EGtEN27Xo= X-Mailgun-Sending-Ip: 198.61.254.9 X-Mailgun-Sid: WyI1YmJiNiIsICJkZXZpY2V0cmVlQHZnZXIua2VybmVsLm9yZyIsICJiZTllNGEiXQ== Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n06.prod.us-west-2.postgun.com with SMTP id 60d2d17f638039e997219931 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 23 Jun 2021 06:15:27 GMT Sender: rajeevny=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id AD7C9C433F1; Wed, 23 Jun 2021 06:15:27 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: rajeevny) by smtp.codeaurora.org (Postfix) with ESMTPSA id 93D9CC433D3; Wed, 23 Jun 2021 06:15:24 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 23 Jun 2021 11:45:24 +0530 From: rajeevny@codeaurora.org To: Doug Anderson Cc: Sam Ravnborg , dri-devel , linux-arm-msm , freedreno , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , LKML , Thierry Reding , Rob Clark , Lyude Paul , Jani Nikula , Rob Herring , Laurent Pinchart , Andrzej Hajda , Daniel Thompson , "Kristian H. Kristensen" , Abhinav Kumar , Sean Paul , Kalyan Thota , Krishna Manikandan , Lee Jones , Jingoo Han , linux-fbdev@vger.kernel.org Subject: Re: [v7 1/5] drm/panel: add basic DP AUX backlight support In-Reply-To: References: <1624099230-20899-1-git-send-email-rajeevny@codeaurora.org> <1624099230-20899-2-git-send-email-rajeevny@codeaurora.org> <20210620093141.GA703072@ravnborg.org> <20210621183828.GA918146@ravnborg.org> Message-ID: X-Sender: rajeevny@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi, On 23-06-2021 00:03, Doug Anderson wrote: > Hi, > > On Mon, Jun 21, 2021 at 11:38 AM Sam Ravnborg wrote: >> >> > > I cannot see why you need the extra check on ->enabled? >> > > Would it be sufficient to check backlight_is_blank() only? >> > >> > This extra check on bl->enabled flag is added to avoid enabling/disabling >> > backlight again if it is already enabled/disabled. >> > Using this flag way can know the transition between backlight blank and >> > un-blank, and decide when to enable/disable the backlight. >> >> My point is that this should really not be needed, as it would cover >> up >> for some other bug whaere we try to do something twice that is not >> needed. But I am less certain here so if you think it is needed, keep >> it as is. > > I haven't tested this myself, but I believe that it is needed. I don't > think the backlight update_status() function is like an enable/disable > function. I believe it can be called more than one time even while the > backlight is disabled. For instance, you can see that > backlight_update_status() just blindly calls through to update the > status. That function can be called for a number of reasons. Perhaps > Rajeev can put some printouts to confirm but I think that if the > backlight is "blanked" for whatever reason and you write to sysfs and > change the backlight level you'll still get called again even though > the backlight is still "disabled". > Yes, sysfs write will always try to update the backlight even though the backlight is "blanked". The "bl->enabled" check is also required to prevent unnecessary calls to drm_edp_backlight_enable() during every backlight level change. To confirm this, I have added few prints in dp_aux_backlight_update_status() function and collected the logs. (Copying the code here to make the review easy) static int dp_aux_backlight_update_status(struct backlight_device *bd) { struct dp_aux_backlight *bl = bl_get_data(bd); u16 brightness = backlight_get_brightness(bd); int ret = 0; + pr_err("%s: brightness %d, _is_blank %d, bl->enabled %d\n", __func__, + brightness, backlight_is_blank(bd), bl->enabled); if (!backlight_is_blank(bd)) { if (!bl->enabled) { + pr_err("%s: enabling backlight\n", __func__); drm_edp_backlight_enable(bl->aux, &bl->info, brightness); bl->enabled = true; return 0; } ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness); } else { if (bl->enabled) { + pr_err("%s: disabling backlight\n", __func__); drm_edp_backlight_disable(bl->aux, &bl->info); bl->enabled = false; } } return ret; } LOGS ==== During boot ----------- [ 4.752188] dp_aux_backlight_update_status: brightness 102, _is_blank 0, bl->enabled 0 [ 4.760447] dp_aux_backlight_update_status: enabling backlight [ 5.503866] dp_aux_backlight_update_status: brightness 102, _is_blank 0, bl->enabled 1 [ 6.897355] dp_aux_backlight_update_status: brightness 103, _is_blank 0, bl->enabled 1 [ 6.938617] dp_aux_backlight_update_status: brightness 104, _is_blank 0, bl->enabled 1 [ 6.980634] dp_aux_backlight_update_status: brightness 105, _is_blank 0, bl->enabled 1 Turning Panel OFF ----------------- localhost ~ # set_power_policy --ac_screen_dim_delay=5 --ac_screen_off_delay=10 localhost ~ # [ 106.555140] dp_aux_backlight_update_status: brightness 145, _is_blank 0, bl->enabled 1 ... ... [ 111.679407] dp_aux_backlight_update_status: brightness 7, _is_blank 0, bl->enabled 1 [ 111.700302] dp_aux_backlight_update_status: brightness 4, _is_blank 0, bl->enabled 1 [ 111.720805] dp_aux_backlight_update_status: brightness 2, _is_blank 0, bl->enabled 1 [ 111.747486] dp_aux_backlight_update_status: brightness 0, _is_blank 1, bl->enabled 1 [ 111.755580] dp_aux_backlight_update_status: disabling backlight [ 111.792344] dp_aux_backlight_update_status: brightness 0, _is_blank 1, bl->enabled 0 Changing brightness from sysfs while panel is off -------------------------------------------------- (it will do nothing) localhost ~ # echo 100 > /sys/class/backlight/dp_aux_backlight/brightness [ 352.754963] dp_aux_backlight_update_status: brightness 0, _is_blank 1, bl->enabled 0 localhost ~ # echo 200 > /sys/class/backlight/dp_aux_backlight/brightness [ 364.708048] dp_aux_backlight_update_status: brightness 0, _is_blank 1, bl->enabled 0 localhost ~ # echo 0 > /sys/class/backlight/dp_aux_backlight/brightness [ 378.850978] dp_aux_backlight_update_status: brightness 0, _is_blank 1, bl->enabled 0 Turning Panel ON ---------------- [ 553.381745] dp_aux_backlight_update_status: brightness 0, _is_blank 0, bl->enabled 0 [ 553.418133] dp_aux_backlight_update_status: enabling backlight [ 553.426397] dp_aux_backlight_update_status: brightness 159, _is_blank 0, bl->enabled 1 ==== Thanks, Rajeev