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From: Matthias Kaehlcke <mka@chromium.org>
To: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc: linux-pwm@vger.kernel.org,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Douglas Anderson <dianders@chromium.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Jingoo Han <jingoohan1@gmail.com>,
	Brian Norris <briannorris@chromium.org>,
	linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org,
	Thierry Reding <thierry.reding@gmail.com>,
	Jacek Anaszewski <jacek.anaszewski@gmail.com>,
	Pavel Machek <pavel@ucw.cz>, Lee Jones <lee.jones@linaro.org>
Subject: Re: [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels
Date: Thu, 13 Jun 2019 15:43:57 +0000	[thread overview]
Message-ID: <20190613154357.GN137143@google.com> (raw)
In-Reply-To: <fd554750-7ec6-73e1-be3a-5bac0749fa0b@collabora.com>

On Thu, Jun 13, 2019 at 11:14:55AM +0200, Enric Balletbo i Serra wrote:
> Hi Matthias,
> 
> On 12/6/19 20:00, Matthias Kaehlcke wrote:
> > With commit 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of
> > LED linearly to human eye") the number of set bits (aka hweight())
> > in the PWM period is used in the heuristic to determine the number
> > of brightness levels, when the brightness table isn't specified in
> > the DT. The number of set bits doesn't provide a reliable clue about
> > the length of the period, instead change the heuristic to:
> > 
> >  nlevels = period / fls(period)
> > 
> > Also limit the maximum number of brightness levels to 4096 to avoid
> > excessively large tables.
> > 
> > With this the number of levels increases monotonically with the PWM
> > period, until the maximum of 4096 levels is reached:
> > 
> > period (ns)    # levels
> > 
> > 100    	       16
> > 500	       62
> > 1000	       111
> > 5000	       416
> > 10000	       769
> > 50000	       3333
> > 100000	       4096
> > 
> > Fixes: 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> Tested on Samsung Chromebook Plus (16-bit pwm)
> 
> Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Thanks!

WARNING: multiple messages have this Message-ID (diff)
From: Matthias Kaehlcke <mka@chromium.org>
To: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc: linux-pwm@vger.kernel.org,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Douglas Anderson <dianders@chromium.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Jingoo Han <jingoohan1@gmail.com>,
	Brian Norris <briannorris@chromium.org>,
	linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org,
	Thierry Reding <thierry.reding@gmail.com>,
	Jacek Anaszewski <jacek.anaszewski@gmail.com>,
	Pavel Machek <pavel@ucw.cz>, Lee Jones <lee.jones@linaro.org>
Subject: Re: [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels
Date: Thu, 13 Jun 2019 08:43:57 -0700	[thread overview]
Message-ID: <20190613154357.GN137143@google.com> (raw)
In-Reply-To: <fd554750-7ec6-73e1-be3a-5bac0749fa0b@collabora.com>

On Thu, Jun 13, 2019 at 11:14:55AM +0200, Enric Balletbo i Serra wrote:
> Hi Matthias,
> 
> On 12/6/19 20:00, Matthias Kaehlcke wrote:
> > With commit 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of
> > LED linearly to human eye") the number of set bits (aka hweight())
> > in the PWM period is used in the heuristic to determine the number
> > of brightness levels, when the brightness table isn't specified in
> > the DT. The number of set bits doesn't provide a reliable clue about
> > the length of the period, instead change the heuristic to:
> > 
> >  nlevels = period / fls(period)
> > 
> > Also limit the maximum number of brightness levels to 4096 to avoid
> > excessively large tables.
> > 
> > With this the number of levels increases monotonically with the PWM
> > period, until the maximum of 4096 levels is reached:
> > 
> > period (ns)    # levels
> > 
> > 100    	       16
> > 500	       62
> > 1000	       111
> > 5000	       416
> > 10000	       769
> > 50000	       3333
> > 100000	       4096
> > 
> > Fixes: 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> Tested on Samsung Chromebook Plus (16-bit pwm)
> 
> Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Thanks!
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dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

WARNING: multiple messages have this Message-ID (diff)
From: Matthias Kaehlcke <mka@chromium.org>
To: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Lee Jones <lee.jones@linaro.org>,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Jingoo Han <jingoohan1@gmail.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Douglas Anderson <dianders@chromium.org>,
	Brian Norris <briannorris@chromium.org>,
	Pavel Machek <pavel@ucw.cz>,
	Jacek Anaszewski <jacek.anaszewski@gmail.com>
Subject: Re: [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels
Date: Thu, 13 Jun 2019 08:43:57 -0700	[thread overview]
Message-ID: <20190613154357.GN137143@google.com> (raw)
In-Reply-To: <fd554750-7ec6-73e1-be3a-5bac0749fa0b@collabora.com>

On Thu, Jun 13, 2019 at 11:14:55AM +0200, Enric Balletbo i Serra wrote:
> Hi Matthias,
> 
> On 12/6/19 20:00, Matthias Kaehlcke wrote:
> > With commit 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of
> > LED linearly to human eye") the number of set bits (aka hweight())
> > in the PWM period is used in the heuristic to determine the number
> > of brightness levels, when the brightness table isn't specified in
> > the DT. The number of set bits doesn't provide a reliable clue about
> > the length of the period, instead change the heuristic to:
> > 
> >  nlevels = period / fls(period)
> > 
> > Also limit the maximum number of brightness levels to 4096 to avoid
> > excessively large tables.
> > 
> > With this the number of levels increases monotonically with the PWM
> > period, until the maximum of 4096 levels is reached:
> > 
> > period (ns)    # levels
> > 
> > 100    	       16
> > 500	       62
> > 1000	       111
> > 5000	       416
> > 10000	       769
> > 50000	       3333
> > 100000	       4096
> > 
> > Fixes: 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> Tested on Samsung Chromebook Plus (16-bit pwm)
> 
> Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Thanks!

  reply	other threads:[~2019-06-13 15:43 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 18:00 [PATCH] backlight: pwm_bl: Fix heuristic to determine number of brightness levels Matthias Kaehlcke
2019-06-12 18:00 ` Matthias Kaehlcke
2019-06-13  9:14 ` Enric Balletbo i Serra
2019-06-13  9:14   ` Enric Balletbo i Serra
2019-06-13 15:43   ` Matthias Kaehlcke [this message]
2019-06-13 15:43     ` Matthias Kaehlcke
2019-06-13 15:43     ` Matthias Kaehlcke
2019-06-21 12:49 ` Daniel Thompson
2019-06-21 12:49   ` Daniel Thompson

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