backlight: mp3309c: Fix LEDs flickering in PWM mode

The mp3309 has two configuration registers, named according to their
address (0x00 and 0x01).
In the second register (0x01), the bit DIMS (Dimming Mode Select) must
be always 0 (zero), in both analog (via I2C commands) and PWM dimming
mode.

In the initial driver version, the DIMS bit was set in PWM mode and
reset in analog mode.
But if the DIMS bit is set in pwm dimming mode and other devices are
connected on the same I2C bus, every I2C commands on the bus generates a
flickering on the LEDs powered by the mp3309c.

This change concerns the chip initialization and does not impact any
existing device-tree configuration.

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240417153105.1794134-2-f.suligoi@asem.it
Signed-off-by: Lee Jones <lee@kernel.org>

diff --git a/drivers/video/backlight/mp3309c.c b/drivers/video/backlight/mp3309c.c
index 016c1296841c4162cb96cd1fd2fae628dfb8de6d..a28036c964aff383fb59488ce3052dc515945be1 100644 (file)
--- a/drivers/video/backlight/mp3309c.c
+++ b/drivers/video/backlight/mp3309c.c
@@ -97,15 +97,10 @@ static int mp3309c_enable_device(struct mp3309c_chip *chip)
 
        /*
         * I2C register #1 - Set working mode:
-        *  - set one of the two dimming mode:
-        *    - PWM dimming using an external PWM dimming signal
-        *    - analog dimming using I2C commands
         *  - enable/disable synchronous mode
         *  - set overvoltage protection (OVP)
         */
        reg_val = 0x00;
-       if (chip->pdata->dimming_mode == DIMMING_PWM)
-               reg_val |= REG_I2C_1_DIMS;
        if (chip->pdata->sync_mode)
                reg_val |= REG_I2C_1_SYNC;
        reg_val |= chip->pdata->over_voltage_protection;