linux-kernel - [PATCH v3] backlight: pwm_bl: Fix brightness levels for non-DT case.

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Message-Id: <20181107085507.26126-1-enric.balletbo@collabora.com>
Date:   Wed,  7 Nov 2018 09:55:07 +0100
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     linux-kernel@...r.kernel.org, robert.jarzmik@...e.fr,
        daniel.thompson@...aro.org, lee.jones@...aro.org
Cc:     kernel@...labora.com, heiko@...ech.de, stable@...r.kernel.org,
        u.kleine-koenig@...gutronix.de, linux-pwm@...r.kernel.org,
        linux-fbdev@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        dri-devel@...ts.freedesktop.org, Jingoo Han <jingoohan1@...il.com>
Subject: [PATCH v3] backlight: pwm_bl: Fix brightness levels for non-DT case.

Commit '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED
linearly to human eye")' allows the possibility to compute a default
brightness table when there isn't the brightness-levels property in the
DT. Unfortunately the changes made broke the pwm backlight for the
non-DT boards.

Usually, the non-DT boards don't pass the brightness levels via platform
data, instead, it sets the max_brightness in their platform data and the
driver calculates the level without a table. The offending patch assumed
that when there is no brightness levels table we should create one, but this
is clearly wrong for the non-DT case.

After this patch the code handles the DT and the non-DT case taking in
consideration also if max_brightness is set or not.

Fixes: 88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")
Cc: <stable@...r.kernel.org>
Reported-by: Robert Jarzmik <robert.jarzmik@...e.fr>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
Tested-by: Robert Jarzmik <robert.jarzmik@...e.fr>
Acked-by: Daniel Thompson <daniel.thompson@...aro.org>
---

Changes in v3:
- Fixed some typos in commit message.
- Removed ' in Fixes tag.

Changes in v2:
- Rebase on top of mainline
- Add Tested-by and Acked-by tags.

 drivers/video/backlight/pwm_bl.c | 41 +++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 678b27063198..f9ef0673a083 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -562,7 +562,30 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 		goto err_alloc;
 	}
 
-	if (!data->levels) {
+	if (data->levels) {
+		/*
+		 * For the DT case, only when brightness levels is defined
+		 * data->levels is filled. For the non-DT case, data->levels
+		 * can come from platform data, however is not usual.
+		 */
+		for (i = 0; i <= data->max_brightness; i++) {
+			if (data->levels[i] > pb->scale)
+				pb->scale = data->levels[i];
+
+			pb->levels = data->levels;
+		}
+	} else if (!data->max_brightness) {
+		/*
+		 * If no brightness levels are provided and max_brightness is
+		 * not set, use the default brightness table. For the DT case,
+		 * max_brightness is set to 0 when brightness levels is not
+		 * specified. For the non-DT case, max_brightness is usually
+		 * set to some value.
+		 */
+
+		/* Get the PWM period (in nanoseconds) */
+		pwm_get_state(pb->pwm, &state);
+
 		ret = pwm_backlight_brightness_default(&pdev->dev, data,
 						       state.period);
 		if (ret < 0) {
@@ -570,13 +593,19 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 				"failed to setup default brightness table\n");
 			goto err_alloc;
 		}
-	}
 
-	for (i = 0; i <= data->max_brightness; i++) {
-		if (data->levels[i] > pb->scale)
-			pb->scale = data->levels[i];
+		for (i = 0; i <= data->max_brightness; i++) {
+			if (data->levels[i] > pb->scale)
+				pb->scale = data->levels[i];
 
-		pb->levels = data->levels;
+			pb->levels = data->levels;
+		}
+	} else {
+		/*
+		 * That only happens for the non-DT case, where platform data
+		 * sets the max_brightness value.
+		 */
+		pb->scale = data->max_brightness;
 	}
 
 	pb->lth_brightness = data->lth_brightness * (state.period / pb->scale);
-- 
2.19.1