linux-kernel - Re: [PATCH] backlight: pwm_bl: Avoid backlight flicker applying initial PWM state

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Message-ID: <20230626150514.GD95170@aspen.lan>
Date:   Mon, 26 Jun 2023 16:05:14 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Helge Deller <deller@....de>, linux-pwm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: pwm_bl: Avoid backlight flicker applying
 initial PWM state

On Thu, Jun 08, 2023 at 04:11:14PM +0200, Philipp Zabel wrote:
> The initial PWM state returned by pwm_init_state() has a duty cycle
> of 0 ns. To avoid backlight flicker when taking over an enabled
> display from the bootloader, skip the initial pwm_apply_state()
> and leave the PWM be until backlight_update_state() will apply the
> state with the desired brightness.

backlight_update_state() uses pwm_get_state() to update the PWM.

Without applying something that came from pwm_init_state() then
we will never adopt the reference values from pwm->args.


Daniel.