From: Alexandru Stan <amstan@chromium.org>
To: "Thierry Reding" <thierry.reding@gmail.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Lee Jones" <lee.jones@linaro.org>,
"Daniel Thompson" <daniel.thompson@linaro.org>,
"Jingoo Han" <jingoohan1@gmail.com>,
"Bartlomiej Zolnierkiewicz" <b.zolnierkie@samsung.com>,
"Heiko Stuebner" <heiko@sntech.de>,
"Rob Herring" <robh+dt@kernel.org>
Cc: Matthias Kaehlcke <mka@chromium.org>,
Douglas Anderson <dianders@chromium.org>,
Enric Balletbo i Serra <enric.balletbo@collabora.com>,
Alexandru Stan <amstan@chromium.org>,
dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: [PATCH 1/3] backlight: pwm_bl: Fix interpolation
Date: Mon, 20 Jul 2020 21:25:20 -0700 [thread overview]
Message-ID: <20200720212502.1.I4dcea1c90e9da3902d466033aa73351e19e49c49@changeid> (raw)
In-Reply-To: <20200721042522.2403410-1-amstan@chromium.org>
Whenever num-interpolated-steps was larger than the distance
between 2 consecutive brightness levels the table would get really
discontinuous. The slope of the interpolation would stick with
integers only and if it was 0 the whole line segment would get skipped.
Example settings:
brightness-levels = <0 1 2 4 8 16 32 64 128 256>;
num-interpolated-steps = <16>;
The distances between 1 2 4 and 8 would be 1, and only starting with 16
it would start to interpolate properly.
Let's change it so there's always interpolation happening, even if
there's no enough points available (read: values in the table would
appear more than once). This should match the expected behavior much
more closely.
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Alexandru Stan <amstan@chromium.org>
---
drivers/video/backlight/pwm_bl.c | 70 ++++++++++++++------------------
1 file changed, 31 insertions(+), 39 deletions(-)
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 82b8d7594701..5193a72305a2 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -235,8 +235,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
struct platform_pwm_backlight_data *data)
{
struct device_node *node = dev->of_node;
- unsigned int num_levels = 0;
- unsigned int levels_count;
+ unsigned int num_levels;
unsigned int num_steps = 0;
struct property *prop;
unsigned int *table;
@@ -265,12 +264,11 @@ static int pwm_backlight_parse_dt(struct device *dev,
if (!prop)
return 0;
- data->max_brightness = length / sizeof(u32);
+ num_levels = length / sizeof(u32);
/* read brightness levels from DT property */
- if (data->max_brightness > 0) {
- size_t size = sizeof(*data->levels) * data->max_brightness;
- unsigned int i, j, n = 0;
+ if (num_levels > 0) {
+ size_t size = sizeof(*data->levels) * num_levels;
data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
if (!data->levels)
@@ -278,7 +276,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
ret = of_property_read_u32_array(node, "brightness-levels",
data->levels,
- data->max_brightness);
+ num_levels);
if (ret < 0)
return ret;
@@ -303,7 +301,13 @@ static int pwm_backlight_parse_dt(struct device *dev,
* between two points.
*/
if (num_steps) {
- if (data->max_brightness < 2) {
+ unsigned int num_input_levels = num_levels;
+ unsigned int i;
+ u32 x1, x2, x;
+ u32 y1, y2;
+ s64 dx, dy;
+
+ if (num_input_levels < 2) {
dev_err(dev, "can't interpolate\n");
return -EINVAL;
}
@@ -313,14 +317,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
* taking in consideration the number of interpolated
* steps between two levels.
*/
- for (i = 0; i < data->max_brightness - 1; i++) {
- if ((data->levels[i + 1] - data->levels[i]) /
- num_steps)
- num_levels += num_steps;
- else
- num_levels++;
- }
- num_levels++;
+ num_levels = (num_input_levels - 1) * num_steps + 1;
dev_dbg(dev, "new number of brightness levels: %d\n",
num_levels);
@@ -332,24 +329,25 @@ static int pwm_backlight_parse_dt(struct device *dev,
table = devm_kzalloc(dev, size, GFP_KERNEL);
if (!table)
return -ENOMEM;
-
- /* Fill the interpolated table. */
- levels_count = 0;
- for (i = 0; i < data->max_brightness - 1; i++) {
- value = data->levels[i];
- n = (data->levels[i + 1] - value) / num_steps;
- if (n > 0) {
- for (j = 0; j < num_steps; j++) {
- table[levels_count] = value;
- value += n;
- levels_count++;
- }
- } else {
- table[levels_count] = data->levels[i];
- levels_count++;
+ /*
+ * Fill the interpolated table[x] = y
+ * by draw lines between each (x1, y1) to (x2, y2).
+ */
+ dx = num_steps;
+ for (i = 0; i < num_input_levels - 1; i++) {
+ x1 = i * dx;
+ x2 = x1 + dx;
+ y1 = data->levels[i];
+ y2 = data->levels[i + 1];
+ dy = y2 - y1;
+
+ for (x = x1; x < x2; x++) {
+ table[x] = y1 +
+ div_s64(dy * (x - x1), dx);
}
}
- table[levels_count] = data->levels[i];
+ /* Fill in the last point, since no line starts here. */
+ table[x2] = y2;
/*
* As we use interpolation lets remove current
@@ -358,15 +356,9 @@ static int pwm_backlight_parse_dt(struct device *dev,
*/
devm_kfree(dev, data->levels);
data->levels = table;
-
- /*
- * Reassign max_brightness value to the new total number
- * of brightness levels.
- */
- data->max_brightness = num_levels;
}
- data->max_brightness--;
+ data->max_brightness = num_levels - 1;
}
return 0;
--
2.27.0
next prev parent reply other threads:[~2020-07-21 4:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 4:25 [PATCH 0/3] PWM backlight interpolation adjustments Alexandru Stan
2020-07-21 4:25 ` Alexandru Stan [this message]
2020-09-04 11:27 ` [PATCH 1/3] backlight: pwm_bl: Fix interpolation Daniel Thompson
2020-07-21 4:25 ` [PATCH 2/3] backlight: pwm_bl: Artificially add 0% during interpolation Alexandru Stan
2020-08-07 8:21 ` daniel
2020-08-13 13:45 ` Daniel Thompson
2020-09-04 11:38 ` Daniel Thompson
2020-09-07 7:50 ` Daniel Vetter
2020-09-09 14:45 ` Daniel Thompson
2020-09-09 15:03 ` Daniel Vetter
2020-09-10 7:47 ` Daniel Vetter
2020-09-09 18:42 ` Alexandru M Stan
2020-08-05 21:04 ` [PATCH 0/3] PWM backlight interpolation adjustments Alexandru M Stan
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200720212502.1.I4dcea1c90e9da3902d466033aa73351e19e49c49@changeid \
--to=amstan@chromium.org \
--cc=b.zolnierkie@samsung.com \
--cc=daniel.thompson@linaro.org \
--cc=dianders@chromium.org \
--cc=dri-devel@lists.freedesktop.org \
--cc=enric.balletbo@collabora.com \
--cc=heiko@sntech.de \
--cc=jingoohan1@gmail.com \
--cc=lee.jones@linaro.org \
--cc=linux-fbdev@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pwm@vger.kernel.org \
--cc=mka@chromium.org \
--cc=robh+dt@kernel.org \
--cc=thierry.reding@gmail.com \
--cc=u.kleine-koenig@pengutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).