Re: [PATCH v3 3/3] backlight: Add Kinetic KTD2801 backlight support

[Daniel Thompson <daniel.thompson@linaro.org>]

On Sat, Jan 20, 2024 at 10:26:45PM +0100, Duje Mihanović wrote:
> KTD2801 is a LED backlight driver IC found in samsung,coreprimevelte.
> The brightness can be set using PWM or the ExpressWire protocol. Add
> support for the KTD2801.
>
> Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>

As Linus W. said, this is looking really nice now. Thanks!

Just a couple of nits below.


> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> index 51387b1ef012..585a5a713759 100644
> --- a/drivers/video/backlight/Kconfig
> +++ b/drivers/video/backlight/Kconfig
> @@ -183,6 +183,14 @@ config BACKLIGHT_KTD253
>  	  which is a 1-wire GPIO-controlled backlight found in some mobile
>  	  phones.
>
> +config BACKLIGHT_KTD2801
> +	tristate "Backlight Driver for Kinetic KTD2801"
> +	depends on GPIOLIB || COMPILE_TEST

As patch 1 feedback, seems odd for the client to be responsible for
this. It should be managed in LEDS_EXPRESSWIRE.


> +	select LEDS_EXPRESSWIRE
> +	help
> +	  Say Y to enable the backlight driver for the Kinetic KTD2801 1-wire
> +	  GPIO-controlled backlight found in Samsung Galaxy Core Prime VE LTE.
> +
>  config BACKLIGHT_KTZ8866
>  	tristate "Backlight Driver for Kinetic KTZ8866"
>  	depends on I2C
> diff --git a/drivers/video/backlight/ktd2801-backlight.c b/drivers/video/backlight/ktd2801-backlight.c
> new file mode 100644
> index 000000000000..7b9d1a93aa71
> --- /dev/null
> +++ b/drivers/video/backlight/ktd2801-backlight.c
> @@ -0,0 +1,143 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Datasheet:
> + * https://www.kinet-ic.com/uploads/web/KTD2801/KTD2801-04b.pdf
> + */
> +#include <linux/backlight.h>
> +#include <linux/bits.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/leds-expresswire.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +
> +/* These values have been extracted from Samsung's driver. */
> +#define KTD2801_EXPRESSWIRE_DETECT_DELAY_US	150
> +#define KTD2801_EXPRESSWIRE_DETECT_US		270
> +#define KTD2801_SHORT_BITSET_US			5
> +#define KTD2801_LONG_BITSET_US			(3 * KTD2801_SHORT_BITSET_US)
> +#define KTD2801_DATA_START_US			5
> +#define KTD2801_END_OF_DATA_LOW_US		10
> +#define KTD2801_END_OF_DATA_HIGH_US		350
> +#define KTD2801_PWR_DOWN_DELAY_US		2600

These are a little pointless now. They are all single use constants
and have little documentary value.

The lack of documentary value is because, for example,
KTD2801_EXPRESSWIRE_DETECT_DELAY_US, is assigned to a structure
field called detect_delay_us.

Likewise I doubt that explicitly stating that long_bitset_us is 3x
bigger than short_bitset_us is important for future driver maintainance.


> +
> +#define KTD2801_DEFAULT_BRIGHTNESS	100
> +#define KTD2801_MAX_BRIGHTNESS		255
> +
> +const struct expresswire_timing ktd2801_timing = {
> +	.poweroff_us = KTD2801_PWR_DOWN_DELAY_US,
> +	.detect_delay_us = KTD2801_EXPRESSWIRE_DETECT_DELAY_US,
> +	.detect_us = KTD2801_EXPRESSWIRE_DETECT_US,
> +	.data_start_us = KTD2801_DATA_START_US,
> +	.short_bitset_us = KTD2801_SHORT_BITSET_US,
> +	.long_bitset_us = KTD2801_LONG_BITSET_US,
> +	.end_of_data_low_us = KTD2801_END_OF_DATA_LOW_US,
> +	.end_of_data_high_us = KTD2801_END_OF_DATA_HIGH_US
> +};
> +
> +struct ktd2801_backlight {
> +	struct expresswire_common_props props;
> +	struct backlight_device *bd;
> +	bool was_on;
> +};
> +
> +static int ktd2801_update_status(struct backlight_device *bd)
> +{
> +	struct ktd2801_backlight *ktd2801 = bl_get_data(bd);
> +	u8 brightness = (u8) backlight_get_brightness(bd);
> +
> +	if (backlight_is_blank(bd)) {
> +		expresswire_power_off(&ktd2801->props);
> +		ktd2801->was_on = false;
> +		return 0;
> +	}
> +
> +	if (!ktd2801->was_on) {
> +		expresswire_enable(&ktd2801->props);
> +		ktd2801->was_on = true;
> +	}
> +
> +	expresswire_start(&ktd2801->props);
> +
> +	for (int i = 7; i >= 0; i--)
> +		expresswire_set_bit(&ktd2801->props, !!(brightness & BIT(i)));

The !! is redundant... but, as previous feedback, I think writing a u8
should be in the library code anyway.

> +	expresswire_end(&ktd2801->props);
> +	return 0;
> +}
> +
> <snip>


Daniel.