Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752389AbeADIXT (ORCPT + 1 other); Thu, 4 Jan 2018 03:23:19 -0500 Received: from fllnx209.ext.ti.com ([198.47.19.16]:53251 "EHLO fllnx209.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751593AbeADIXQ (ORCPT ); Thu, 4 Jan 2018 03:23:16 -0500 Subject: Re: [RFC] pwm-backlight: Allow backlight to remain disabled on boot To: hl , Thierry Reding , Jingoo Han , Bryan Wu , Lee Jones CC: Mark Rutland , , , Russell King , Brian Norris , Pawel Moll , Ian Campbell , , Rob Herring , Doug Anderson , Matthias Kaehlcke , Tomi Valkeinen , Kumar Gala , Eric Miao , Jean-Christophe Plagniol-Villard , References: <1406806970-12561-1-git-send-email-thierry.reding@gmail.com> <6b14a283-0ded-e22c-8f81-5c241ad57463@rock-chips.com> From: Peter Ujfalusi Message-ID: <6a77b1bc-29fa-2bc5-baeb-0cba8747137a@ti.com> Date: Thu, 4 Jan 2018 10:22:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <6b14a283-0ded-e22c-8f81-5c241ad57463@rock-chips.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: Hi, On 2018-01-04 04:18, hl wrote: > Hi All, > >     Since many panel power sequence request backlight stay disable > > before panel power ready, but with now pwm-backlight drvier, it default to > > enable backlight when pwm-backlight probe, it mess up the panel power > sequence. > > So we need this patch. This patch have been fly for a long time, does > anyone have plan > > to merge it? you should not need this anymore since we have: 892c7788c724backlight: pwm_bl: Fix GPIO out for unimplemented .get_direction() d1b812945750 backlight: pwm_bl: Check the PWM state for initial backlight power state 7613c922315e backlight: pwm_bl: Move the checks for initial power state to a separate function With these in place the backlight will be kept disabled if it was disabled during boot _if_ you have booted via DT _and_ you have a phandle pointing to the backlight node (implying that the backlight is managed by the display driver). > > > On Thursday, July 31, 2014 07:42 PM, Thierry Reding wrote: >> From: Thierry Reding >> >> The default for backlight devices is to be enabled immediately when >> registering with the backlight core. This can be useful for setups that >> use a simple framebuffer device and where the backlight cannot otherwise >> be hooked up to the panel. >> >> However, when dealing with more complex setups, such as those of recent >> ARM SoCs, this can be problematic. Since the backlight is usually setup >> separately from the display controller, the probe order is not usually >> deterministic. That can lead to situations where the backlight will be >> powered up and the panel will show an uninitialized framebuffer. >> >> Furthermore, subsystems such as DRM have advanced functionality to set >> the power mode of a panel. In order to allow such setups to power up the >> panel at exactly the right moment, a way is needed to prevent the >> backlight core from powering the backlight up automatically when it is >> registered. >> >> This commit introduces a new boot_off field in the platform data (and >> also implements getting the same information from device tree). When set >> the initial backlight power mode will be set to "off". >> >> Signed-off-by: Thierry Reding >> --- >> I've been meaning to send this for a while but was always holding back >> because of the indoctrination that this type of configuration shouldn't >> be part of device tree. However this issue was recently raised again in >> the context of power up sequences for display panels. As described above >> the issue is that panel datasheets recommend that the backlight attached >> to a panel be turned on at the very last step to avoid visual glitches >> during the panel's power up sequence. With the current implementation it >> is typical for the backlight to be probed before the display panel. That >> has, in many cases, the side-effect of enabling the backlight, therefore >> making the screen content visible before it's actually initialized. >> >> Some panels come up with random garbage when uninitialized, others show >> all white. With some luck the panel will be all black and users won't >> really notice. >> >> This patch is an attempt to enable boards to override the default of >> turning on the backlight for the pwm-backlight driver. I'm not sure if >> there was a specific reason to turn on the backlight by default when >> this driver was initially written, but the fact is that since it has >> pretty much always been like this we can't really go and change the >> default, otherwise a lot of people may end up with no backlight and no >> clue as to how to enable it. So the only reasonable thing we can do is >> to keep the old behaviour and give new boards a way to override it if >> they know that some other part of the stack will enable it at the right >> moment. >> >>   .../devicetree/bindings/video/backlight/pwm-backlight.txt         | 1 + >>   drivers/video/backlight/pwm_bl.c                                  | >> 8 ++++++++ >>   include/linux/pwm_backlight.h                                     | >> 2 ++ >>   3 files changed, 11 insertions(+) >> >> diff --git >> a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt >> b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt >> index 764db86d441a..65e001a1733d 100644 >> --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt >> +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt >> @@ -17,6 +17,7 @@ Optional properties: >>                  "pwms" property (see PWM binding[0]) >>     - enable-gpios: contains a single GPIO specifier for the GPIO >> which enables >>                     and disables the backlight (see GPIO binding[1]) >> +  - backlight-boot-off: keep the backlight disabled on boot >>     [0]: Documentation/devicetree/bindings/pwm/pwm.txt >>   [1]: Documentation/devicetree/bindings/gpio/gpio.txt >> diff --git a/drivers/video/backlight/pwm_bl.c >> b/drivers/video/backlight/pwm_bl.c >> index d7a3d13e72ec..62adfc9d37a7 100644 >> --- a/drivers/video/backlight/pwm_bl.c >> +++ b/drivers/video/backlight/pwm_bl.c >> @@ -173,6 +173,8 @@ static int pwm_backlight_parse_dt(struct device *dev, >>           data->max_brightness--; >>       } >>   +    data->boot_off = of_property_read_bool(node, >> "backlight-boot-off"); >> + >>       return 0; >>   } >>   @@ -317,6 +319,12 @@ static int pwm_backlight_probe(struct >> platform_device *pdev) >>       } >>         bl->props.brightness = data->dft_brightness; >> + >> +    if (data->boot_off) >> +        bl->props.power = FB_BLANK_POWERDOWN; >> +    else >> +        bl->props.power = FB_BLANK_UNBLANK; >> + >>       backlight_update_status(bl); >>         platform_set_drvdata(pdev, bl); >> diff --git a/include/linux/pwm_backlight.h >> b/include/linux/pwm_backlight.h >> index efdd9227a49c..1fc14989da4a 100644 >> --- a/include/linux/pwm_backlight.h >> +++ b/include/linux/pwm_backlight.h >> @@ -15,6 +15,8 @@ struct platform_pwm_backlight_data { >>       unsigned int *levels; >>       /* TODO remove once all users are switched to gpiod_* API */ >>       int enable_gpio; >> +    bool boot_off; >> + >>       int (*init)(struct device *dev); >>       int (*notify)(struct device *dev, int brightness); >>       void (*notify_after)(struct device *dev, int brightness); > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel - Péter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. 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