From: Daniel Thompson <daniel.thompson@linaro.org>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Lee Jones <lee@kernel.org>, Jingoo Han <jingoohan1@gmail.com>,
Liam Girdwood <lgirdwood@gmail.com>,
Mark Brown <broonie@kernel.org>,
Thierry Reding <thierry.reding@gmail.com>,
Helge Deller <deller@gmx.de>,
linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-fbdev@vger.kernel.org, kernel@pengutronix.de
Subject: Re: [PATCH v2 2/2] backlight: pwm_bl: Don't rely on a disabled PWM emiting inactive state
Date: Fri, 20 Jan 2023 15:04:38 +0000 [thread overview]
Message-ID: <Y8qthjHiCTO3OK/R@aspen.lan> (raw)
In-Reply-To: <20230120120018.161103-3-u.kleine-koenig@pengutronix.de>
On Fri, Jan 20, 2023 at 01:00:18PM +0100, Uwe Kleine-König wrote:
> Most but not all PWMs drive the PWM pin to its inactive state when
> disabled. However if there is no enable_gpio and no regulator the PWM
> must drive the inactive state to actually disable the backlight.
>
> So keep the PWM on in this case.
>
> Note that to determine if there is a regulator some effort is required
> because it might happen that there isn't actually one but the regulator
> core gave us a dummy. (A nice side effect is that this makes the
> regulator actually optional even on fully constrained systems.)
>
> This fixes backlight disabling e.g. on i.MX6 when an inverted PWM is
> used.
>
> Hint for the future: If this change results in a regression, the bug is
> in the lowlevel PWM driver.
:-)
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Thanks for the changes. Looks good:
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Daniel.
next prev parent reply other threads:[~2023-01-20 15:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-20 12:00 [PATCH v2 0/2] backlight: pwm_bl: Two PWM releated changes Uwe Kleine-König
2023-01-20 12:00 ` [PATCH v2 1/2] backlight: pwm_bl: Configure pwm only once per backlight toggle Uwe Kleine-König
2023-01-20 17:07 ` Lee Jones
2023-01-20 12:00 ` [PATCH v2 2/2] backlight: pwm_bl: Don't rely on a disabled PWM emiting inactive state Uwe Kleine-König
2023-01-20 15:04 ` Daniel Thompson [this message]
2023-01-20 17:07 ` Lee Jones
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