linux-kernel - Re: [PATCH 2/3] backlight: pwm_bl: Artificially add 0% during interpolation

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Date:   Fri, 7 Aug 2020 10:21:13 +0200
From:   daniel@...ll.ch
To:     unlisted-recipients:; (no To-header on input)
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Rob Herring <robh+dt@...nel.org>, linux-pwm@...r.kernel.org,
        linux-fbdev@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>
Subject: Re: [PATCH 2/3] backlight: pwm_bl: Artificially add 0% during
 interpolation

On Mon, Jul 20, 2020 at 09:25:21PM -0700, Alexandru Stan wrote:
> Some displays need the low end of the curve cropped in order to make
> them happy. In that case we still want to have the 0% point, even though
> anything between 0% and 5%(example) would be skipped.
> 
> Signed-off-by: Alexandru Stan <amstan@...omium.org>
> ---
> 
>  drivers/video/backlight/pwm_bl.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index 5193a72305a2..b24711ddf504 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -349,6 +349,14 @@ static int pwm_backlight_parse_dt(struct device *dev,
>  			/* Fill in the last point, since no line starts here. */
>  			table[x2] = y2;
>  
> +			/*
> +			 * If we don't start at 0 yet we're increasing, assume
> +			 * the dts wanted to crop the low end of the range, so
> +			 * insert a 0 to provide a display off mode.
> +			 */
> +			if (table[0] > 0 && table[0] < table[num_levels - 1])
> +				table[0] = 0;

Isn't that what the enable/disable switch in backlights are for? There's
lots of backligh drivers (mostly the firmware variety) where setting the
backlight to 0 does not shut it off, it's just the lowest setting.

But I've not been involved in the details of these discussions.
-Daniel

> +
>  			/*
>  			 * As we use interpolation lets remove current
>  			 * brightness levels table and replace for the
> -- 
> 2.27.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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