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From: "Noralf Trønnes" <>
To: Marek Vasut <>,
	Daniel Thompson <>
	Meghana Madhyastha <>,
	Sean Paul <>,
	Thierry Reding <>
Subject: Re: [PATCH] video: backlight: Only set maximum brightness for gpio-backlight
Date: Fri, 9 Jul 2021 15:25:29 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Den 09.07.2021 15.19, skrev Marek Vasut:
> On 7/9/21 1:03 PM, Daniel Thompson wrote:
>> On Thu, Jul 08, 2021 at 11:10:58AM +0200, Marek Vasut wrote:
>>> The note in c2adda27d202f ("video: backlight: Add of_find_backlight
>>> helper
>>> in backlight.c") says that gpio-backlight uses brightness as power
>>> state.
>>> Other backlight drivers do not, so limit this workaround to
>>> gpio-backlight.
>>> This fixes the case where e.g. pwm-backlight can perfectly well be
>>> set to
>>> brightness 0 on boot in DT, which without this patch leads to the
>>> display
>>> brightness to be max instead of off.
>>> Fixes: c2adda27d202f ("video: backlight: Add of_find_backlight helper
>>> in backlight.c")
>>> Signed-off-by: Marek Vasut <>
>>> Cc: Daniel Thompson <>
>>> Cc: Meghana Madhyastha <>
>>> Cc: Noralf Trønnes <>
>>> Cc: Sean Paul <>
>>> Cc: Thierry Reding <>
>> I have to admit that this patch really does makes it clear just how
>> nasty the hack in of_find_backlight() currently is.
>> Moreover I think it is also be obsolete. gpio-backlight power mode
>> handling was pretty broken when this code was introduced. It was fixed
>> in 2019 by ec665b756e6f ("backlight: gpio backlight: Correct initial
>> power state handling") by trying to match the behaviour of PWM
>> backlight.  The new code always sets the brightness to 1 so I think we
>> can just remove the hack from of_find_backlight() since I think it is
>> unreachable.
> I assume by "new code" you mean the fixed gpio-backlight driver ?
> Dropping the whole code after the Note: is fine by me.

I haven't actually tested it, but when I saw the patch that Daniel
points to, it looked like this work around could be removed.
I haven't got time to tests it, but I will ack a patch that removes the


      reply	other threads:[~2021-07-09 13:25 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-08  9:10 Marek Vasut
2021-07-09 11:03 ` Daniel Thompson
2021-07-09 13:19   ` Marek Vasut
2021-07-09 13:25     ` Noralf Trønnes [this message]

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