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Date: Tue, 6 Oct 2026 11:11:04 +0100
From: Daniel Thompson <danielt@kernel.org>
To: david@ixit.cz
Cc: Lee Jones <lee@kernel.org>, Jingoo Han <jingoohan1@gmail.com>,
	Helge Deller <deller@gmx.de>, Kiran Gunda <quic_kgunda@quicinc.com>,
	Marco Mattiolo <marco.mattiolo@hotmail.it>,
	=?iso-8859-1?B?QmFybmFi4XMgQ3rpbeFu?= <barnabas.czeman@mainlining.org>,
	linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	phone-devel@vger.kernel.org,
	Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>,
	Joel Selvaraj <foss@joelselvaraj.com>
Subject: Re: [PATCH v4 4/4] backlight: qcom-wled: Read back the programmed
 brightness at probe
Message-ID: <asTJOGXnq3pixevl@aspen.lan>
References: <20260921-qcom-wled-backlight-v4-0-bab8c7ef73cb@ixit.cz>
 <20260921-qcom-wled-backlight-v4-4-bab8c7ef73cb@ixit.cz>
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In-Reply-To: <20260921-qcom-wled-backlight-v4-4-bab8c7ef73cb@ixit.cz>

On Mon, Sep 21, 2026 at 12:46:25PM +0200, David Heidelberg via B4 Relay wrote:
> From: David Heidelberg <david@ixit.cz>
>
> Since the previous change wled_probe() seeds wled->brightness from
> MOD_EN, but with default-brightness rather than the level the hardware
> is actually driving, so a backlight left lit by the bootloader still
> visibly steps on the first update, and actual_brightness reports the
> last value written rather than what the panel shows.
>
> Add wled_read_brightness(), which returns 0 when MOD_EN is clear and
> otherwise reads the brightness register the matching
> wledN_set_brightness() writes: the first enabled string on WLED3 and
> WLED4, the selected modulator on WLED5. Use it to seed both
> wled->brightness and the initial backlight property, and expose it as
> backlight_ops.get_brightness so that actual_brightness reflects the
> hardware too.
>
> A module that is enabled with the brightness registers at zero, which
> wled4_setup() and wled_auto_string_detection() can leave behind on a
> cold boot, now reads back as off. The OVP interrupt is then armed by the
> first brightness update rather than from probe, which is what happens
> on every other board where the module starts out disabled.
>
> Suggested-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> Assisted-by: LLM
> Signed-off-by: David Heidelberg <david@ixit.cz>

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


Daniel.