linux-kernel - Re: [PATCH] backlight: pwm_bl: apply the initial backlight state with sane defaults

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Message-ID: <aQNRK5ksNDMMve0x@aspen.lan>
Date: Thu, 30 Oct 2025 11:51:07 +0000
From: Daniel Thompson <danielt@...nel.org>
To: Michael Grzeschik <m.grzeschik@...gutronix.de>
Cc: Uwe Kleine-König <ukleinek@...nel.org>,
	Lee Jones <lee@...nel.org>, Jingoo Han <jingoohan1@...il.com>,
	Helge Deller <deller@....de>, Pengutronix <kernel@...gutronix.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: apply the initial backlight state
 with sane defaults

On Thu, Jul 31, 2025 at 10:47:18AM +0200, Michael Grzeschik wrote:
> Currently when calling pwm_apply_might_sleep in the probe routine
> the pwm will be configured with an not fully defined state.
>
> The duty_cycle is not yet set in that moment. There is a final
> backlight_update_status call that will have a properly setup state.
> However this change in the backlight can create a short flicker if the
> backlight was already preinitialised.
>
> We fix the flicker by moving the pwm_apply after the default duty_cycle
> can be calculated.
>
> Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>

Reviewed-by: Daniel Thompson (RISCstar) <danielt@...nel.org>


Daniel.