linux-kernel - Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

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Date: Fri, 19 Jan 2024 10:02:33 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Duje Mihanović <duje.mihanovic@...le.hr>
Cc: Lee Jones <lee@...nel.org>, Daniel Thompson <daniel.thompson@...aro.org>, 
	Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Helge Deller <deller@....de>, Karel Balej <balejk@...fyz.cz>, ~postmarketos/upstreaming@...ts.sr.ht, 
	dri-devel@...ts.freedesktop.org, linux-leds@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

Hi Duje,

thanks for your patch!

On Thu, Jan 18, 2024 at 6:33 PM Duje Mihanović <duje.mihanovic@...le.hr> wrote:

> Add driver for the Kinetic KTD2801 backlight driver.>
> Signed-off-by: Duje Mihanović <duje.mihanovic@...le.hr>

Add some commit message?

> +#include <linux/backlight.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/of.h>

I don't think you need <linux/of.h>, the compatible table works without
that (is in the device driver core).

> +/* These values have been extracted from Samsung's driver. */
> +#define KTD2801_EXPRESSWIRE_DETECT_DELAY_US    150
> +#define KTD2801_EXPRESSWIRE_DETECT_US          270
> +#define KTD2801_LOW_BIT_HIGH_TIME_US           5
> +#define KTD2801_LOW_BIT_LOW_TIME_US            (4 * KTD2801_HIGH_BIT_LOW_TIME_US)
> +#define KTD2801_HIGH_BIT_LOW_TIME_US           5
> +#define KTD2801_HIGH_BIT_HIGH_TIME_US          (4 * KTD2801_HIGH_BIT_LOW_TIME_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
> +
> +#define KTD2801_DEFAULT_BRIGHTNESS     100
> +#define KTD2801_MAX_BRIGHTNESS         255
> +
> +struct ktd2801_backlight {
> +       struct backlight_device *bd;
> +       struct gpio_desc *gpiod;
> +       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)) {
> +               gpiod_set_value(ktd2801->gpiod, 0);
> +               udelay(KTD2801_PWR_DOWN_DELAY_US);

That's 2600 us, a pretty long delay in a hard loop or delay timer!

Can you use usleep_range() instead, at least for this one?

> +       for (int i = 0; i < 8; i++) {
> +               u8 next_bit = (brightness & 0x80) >> 7;

I would just:

#include <linux/bits.h>

bool next_bit = !!(brightness & BIT(7));

Yours,
Linus Walleij