From patchwork Thu Oct 17 08:10:59 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= X-Patchwork-Id: 1178351 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=linux-pwm-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 46v21F74f7z9sP3 for ; Thu, 17 Oct 2019 19:11:13 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408162AbfJQILM (ORCPT ); Thu, 17 Oct 2019 04:11:12 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:40121 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392882AbfJQILL (ORCPT ); Thu, 17 Oct 2019 04:11:11 -0400 Received: from dude.hi.pengutronix.de ([2001:67c:670:100:1d::7]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1iL0sH-0005ka-6T; Thu, 17 Oct 2019 10:11:09 +0200 Received: from ukl by dude.hi.pengutronix.de with local (Exim 4.92) (envelope-from ) id 1iL0sG-0002A7-6d; Thu, 17 Oct 2019 10:11:08 +0200 From: =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= To: Adam Ford , Enric Balletbo i Serra , Daniel Thompson , Lee Jones , Jingoo Han Cc: Thierry Reding , linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, kernel@pengutronix.de Subject: [PATCH] backlight: pwm_bl: configure pwm only once per backlight toggle Date: Thu, 17 Oct 2019 10:10:59 +0200 Message-Id: <20191017081059.31761-1-u.kleine-koenig@pengutronix.de> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::7 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-pwm@vger.kernel.org Sender: linux-pwm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pwm@vger.kernel.org A previous change in the pwm core (namely 01ccf903edd6 ("pwm: Let pwm_get_state() return the last implemented state")) changed the semantic of pwm_get_state() and disclosed an (as it seems) common problem in lowlevel PWM drivers. By not relying on the period and duty cycle being retrievable from a disabled PWM this type of problem is worked around. Apart from this issue only calling the pwm_get_state/pwm_apply_state combo once is also more effective. Signed-off-by: Uwe Kleine-König Signed-off-by: Thierry Reding Signed-off-by: Thierry Reding Tested-by: Adam Ford #imx6q-logicpd Tested-by: Michal Vokáč --- Hello, There are now two reports about 01ccf903edd6 breaking a backlight. As far as I understand the problem this is a combination of the backend pwm driver yielding surprising results and the pwm-bl driver doing things more complicated than necessary. So I guess this patch works around these problems. Still it would be interesting to find out the details in the imx driver that triggers the problem. So Adam, can you please instrument the pwm-imx27 driver to print *state at the beginning of pwm_imx27_apply() and the end of pwm_imx27_get_state() and provide the results? Note I only compile tested this change. Best regards Uwe drivers/video/backlight/pwm_bl.c | 34 +++++++++++--------------------- 1 file changed, 12 insertions(+), 22 deletions(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 746eebc411df..ddebd62b3978 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -42,10 +42,8 @@ struct pwm_bl_data { static void pwm_backlight_power_on(struct pwm_bl_data *pb) { - struct pwm_state state; int err; - pwm_get_state(pb->pwm, &state); if (pb->enabled) return; @@ -53,9 +51,6 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb) if (err < 0) dev_err(pb->dev, "failed to enable power supply\n"); - state.enabled = true; - pwm_apply_state(pb->pwm, &state); - if (pb->post_pwm_on_delay) msleep(pb->post_pwm_on_delay); @@ -67,40 +62,27 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb) static void pwm_backlight_power_off(struct pwm_bl_data *pb) { - struct pwm_state state; - - pwm_get_state(pb->pwm, &state); - if (!pb->enabled) - return; - if (pb->enable_gpio) gpiod_set_value_cansleep(pb->enable_gpio, 0); if (pb->pwm_off_delay) msleep(pb->pwm_off_delay); - state.enabled = false; - state.duty_cycle = 0; - pwm_apply_state(pb->pwm, &state); - regulator_disable(pb->power_supply); pb->enabled = false; } -static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness) +static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness, struct pwm_state *state) { unsigned int lth = pb->lth_brightness; - struct pwm_state state; u64 duty_cycle; - pwm_get_state(pb->pwm, &state); - if (pb->levels) duty_cycle = pb->levels[brightness]; else duty_cycle = brightness; - duty_cycle *= state.period - lth; + duty_cycle *= state->period - lth; do_div(duty_cycle, pb->scale); return duty_cycle + lth; @@ -122,12 +104,20 @@ static int pwm_backlight_update_status(struct backlight_device *bl) if (brightness > 0) { pwm_get_state(pb->pwm, &state); - state.duty_cycle = compute_duty_cycle(pb, brightness); + state.duty_cycle = compute_duty_cycle(pb, brightness, &state); + state.enabled = true; pwm_apply_state(pb->pwm, &state); + pwm_backlight_power_on(pb); - } else + } else { pwm_backlight_power_off(pb); + pwm_get_state(pb->pwm, &state); + state.enabled = false; + state.duty_cycle = 0; + pwm_apply_state(pb->pwm, &state); + } + if (pb->notify_after) pb->notify_after(pb->dev, brightness);