From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT Date: Mon, 24 Jun 2019 11:54:08 -0700 Message-ID: <20190624185408.GB137143@google.com> References: <20190613194326.180889-1-mka@chromium.org> <20190613194326.180889-5-mka@chromium.org> <9ea1bb40-95a6-7a67-a8a6-ecc77a70e547@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <9ea1bb40-95a6-7a67-a8a6-ecc77a70e547@linaro.org> Sender: linux-kernel-owner@vger.kernel.org To: Daniel Thompson Cc: Thierry Reding , Lee Jones , Jingoo Han , Bartlomiej Zolnierkiewicz , linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Enric Balletbo i Serra , Douglas Anderson , Brian Norris , Pavel Machek , Jacek Anaszewski List-Id: dri-devel@lists.freedesktop.org Hi Daniel, On Fri, Jun 21, 2019 at 02:10:19PM +0100, Daniel Thompson wrote: > On 13/06/2019 20:43, Matthias Kaehlcke wrote: > > Check if a brightness curve specified in the device tree is linear or > > not and set the corresponding property accordingly. This makes the > > scale type available to userspace via the 'scale' sysfs attribute. > > > > To determine if a curve is linear it is compared to a interpolated linear > > curve between min and max brightness. The curve is considered linear if > > no value deviates more than +/-5% of ${brightness_range} from their > > interpolated value. > > > > Signed-off-by: Matthias Kaehlcke > > --- > > drivers/video/backlight/pwm_bl.c | 25 +++++++++++++++++++++++++ > > 1 file changed, 25 insertions(+) > > > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > > index f067fe7aa35d..912407b6d67f 100644 > > --- a/drivers/video/backlight/pwm_bl.c > > +++ b/drivers/video/backlight/pwm_bl.c > > @@ -404,6 +404,26 @@ int pwm_backlight_brightness_default(struct device *dev, > > } > > #endif > > +static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data) > > +{ > > + unsigned int nlevels = data->max_brightness + 1; > > + unsigned int min_val = data->levels[0]; > > + unsigned int max_val = data->levels[nlevels - 1]; > > + unsigned int slope = (100 * (max_val - min_val)) / nlevels; > > Why 100 (rather than a power of 2)? I guess it came from the decimal part of my brain, I can change it to 128 ;-) > It would also be good to have a comment here saying what the maximum > quantization error is. Doesn't have to be over complex just mentioning > something like the following (assuming you agree that its true ;-) ): > > Multiplying by XXX means that even in pathalogical cases such as > (max_val - min_val) == nlevels then the error at max_val is less than > 1%. Sounds good, thanks for the suggestion! > With a suitable comment in the fixed point code: > Acked-by: Daniel Thompson Thanks