Re: [PATCH 15/16] backlight: remove pandora_bl

Am 10.08.2026 um 15:23 schrieb H. Nikolaus Schaller [off-list ref]:

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Am 10.08.2026 um 14:39 schrieb Andreas Kemnade [off-list ref]:

On Mon, 10 Aug 2026 12:45:16 +0200
"H. Nikolaus Schaller" [off-list ref] wrote:

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Hi Daniel,

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Am 10.08.2026 um 12:35 schrieb Daniel Thompson [off-list ref]:

On Sat, Jul 11, 2026 at 08:02:02AM +0200, H. Nikolaus Schaller wrote:  

quoted

Retire the platform specific pandora backlight driver since
it can now be replaced by twl_pm and device tree.

Signed-off-by: H. Nikolaus Schaller <redacted>  

Yay!

Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>  

Well, there were some good comments by Sahiko to the prerequisites of this patch,
because it has one speciality the PWM BL driver does not handle (avoid
interpretation of PWM signals as W1 protocol).

Here is the report: https://sashiko.dev/#/patchset/cover.1783749722.git.hns@goldelico.com?part=15

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I haven't found time to work on this, so we can't remove this yet.

In the end it may either remain a pandora_bl driver (converted to DT)
or become a patch for something else.

But then it is a TPS61161 on top of PWM, not a pandora driver.
And then there might be just a quirk for that chip in the pwm_bl using
triggered by a compatible. I guess the quirk is this:


if (priv->old_state == PANDORABL_WAS_OFF) {
- /*
- * set PWM duty cycle to max. TPS61161 seems to use this
- * to calibrate it's PWM sensitivity when it starts.
- */
- twl_i2c_write_u8(TWL_MODULE_PWM, MAX_VALUE, TWL_PWM0_OFF);
-
- /* first enable clock, then PWM0 out */
- twl_i2c_read_u8(TWL4030_MODULE_INTBR, &r, TWL_INTBR_GPBR1);
- r &= ~PWM0_ENABLE;
- r |= PWM0_CLK_ENABLE;
- twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_GPBR1);
- r |= PWM0_ENABLE;
- twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_GPBR1);
-
- /*
- * TI made it very easy to enable digital control, so easy that
- * it often triggers unintentionally and disabes PWM control,
- * so wait until 1 wire mode detection window ends.
- */
- usleep_range(2000, 10000);
- }

Exactly. The Sashiko comment to this section was:

When switching to the generic pwm-backlight driver, how is the TPS61161
initialized into PWM mode? Because the TPS61161 shares its EN pin for both 1-wire
EasyScale digital control and PWM control, the removed pandora_bl driver included this
hardware workaround to force a 100% PWM duty cycle and sleep for 2-10ms at
startup. Without this initialization pulse, could the TPS61161 misinterpret the initial
PWM signal as a 1-wire EasyScale command and disable PWM control, preventing
the backlight from turning on properly?

Well, I didn't see this but it would be on the safe side to have it.

Yes that is what I mean. It needs to be ported somewhere. If it can be ported to
some compatible = "pwm_bl_for_tps61161" or what fits best it will be fine. Or it
could be in some compatible = "pandora_bl" driver.

Has to be worked out when the development machines are not blocked by 3 or 4 other
projects already running in parallel :)

Nevertheless I did a quick look into the pandora_bl driver structure.

Here are my findings:
- the code fragment is part of pandora_backlight_update_status()
- priv->old_state remembers if brighness was set to 0 or not
- so this code triggers on any change from bright = 0 to bright > 0
- the pandora_bl driver is the only one to use TWL_MODULE_PWM besides twl-pwm

So the most natural way of transplanting this appears to me:
- add this logic to the twl-pwm driver
- add a propery to escribe this special need (e.g. "disable-easyscale")
- use this to triger the extra code in case this flag is set
- and if the pwm duty cycle changes from permanently off to real PWM
- this should obviously go into twl_pwm_config() to detect through duty_ns
- alternativey it might be possible to handle everything in twl4030_pwm_enable

Suggestions welcome.

BR,
Nikolaus