linux-kernel - Re: [PATCH 2/4] backlight: ktz8866: add slave handler

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Message-ID: <eb23737f-5b6c-47fd-8b39-637e059bd5f1@kernel.org>
Date: Mon, 7 Apr 2025 12:00:26 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Pengyu Luo <mitltlatltl@...il.com>, Jianhua Lu <lujianhua000@...il.com>,
 Lee Jones <lee@...nel.org>, Daniel Thompson <danielt@...nel.org>,
 Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Helge Deller <deller@....de>
Cc: 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 2/4] backlight: ktz8866: add slave handler

On 07/04/2025 11:51, Pengyu Luo wrote:
> Kinetic ktz8866, found in many android devices, nowadays, some oem use
> dual ktz8866 to support a larger panel and  higher brightness, original
> driver would only handle half backlight region on these devices,
> registering it twice is unreasonable, so adding the slave handler to
> support it.
> 
> Note that, none of the devices supported by upstream require this, the
> devices using this is porting.
> 
> Signed-off-by: Pengyu Luo <mitltlatltl@...il.com>
> ---
>  drivers/video/backlight/ktz8866.c | 68 +++++++++++++++++++++++++++----
>  1 file changed, 59 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/video/backlight/ktz8866.c b/drivers/video/backlight/ktz8866.c
> index 351c2b4d6..017ad80dd 100644
> --- a/drivers/video/backlight/ktz8866.c
> +++ b/drivers/video/backlight/ktz8866.c
> @@ -3,6 +3,9 @@
>   * Backlight driver for the Kinetic KTZ8866
>   *
>   * Copyright (C) 2022, 2023 Jianhua Lu <lujianhua000@...il.com>
> + *
> + * Apr 2025 - Pengyu Luo <mitltlatltl@...il.com>
> + *	Added handling for dual KTZ8866(master and slave)
>   */
>  
>  #include <linux/backlight.h>
> @@ -43,11 +46,17 @@
>  #define LCD_BIAS_EN 0x9F
>  #define PWM_HYST 0x5
>  
> +struct ktz8866_slave {
> +	struct i2c_client *client;
> +	struct regmap *regmap;
> +};
> +
>  struct ktz8866 {
>  	struct i2c_client *client;
>  	struct regmap *regmap;
> -	bool led_on;
>  	struct gpio_desc *enable_gpio;
> +	struct ktz8866_slave *slave;
> +	bool led_on;
>  };
>  
>  static const struct regmap_config ktz8866_regmap_config = {
> @@ -56,16 +65,22 @@ static const struct regmap_config ktz8866_regmap_config = {
>  	.max_register = REG_MAX,
>  };
>  
> -static int ktz8866_write(struct ktz8866 *ktz, unsigned int reg,
> -			 unsigned int val)
> +static void ktz8866_write(struct ktz8866 *ktz, unsigned int reg,
> +			  unsigned int val)
>  {
> -	return regmap_write(ktz->regmap, reg, val);
> +	regmap_write(ktz->regmap, reg, val);
> +
> +	if (ktz->slave)
> +		regmap_write(ktz->slave->regmap, reg, val);
>  }
>  
> -static int ktz8866_update_bits(struct ktz8866 *ktz, unsigned int reg,
> -			       unsigned int mask, unsigned int val)
> +static void ktz8866_update_bits(struct ktz8866 *ktz, unsigned int reg,
> +				unsigned int mask, unsigned int val)
>  {
> -	return regmap_update_bits(ktz->regmap, reg, mask, val);
> +	regmap_update_bits(ktz->regmap, reg, mask, val);
> +
> +	if (ktz->slave)
> +		regmap_update_bits(ktz->slave->regmap, reg, mask, val);
>  }
>  
>  static int ktz8866_backlight_update_status(struct backlight_device *backlight_dev)
> @@ -124,10 +139,41 @@ static void ktz8866_init(struct ktz8866 *ktz)
>  		ktz8866_write(ktz, LCD_BIAS_CFG1, LCD_BIAS_EN);
>  }
>  
> +static int ktz8866_slave_register(struct ktz8866 *ktz)
> +{
> +	struct device *dev = &ktz->client->dev;
> +	struct ktz8866_slave *slave;
> +	struct i2c_client *client;
> +	struct device_node *np;
> +
> +	np = of_find_compatible_node(NULL, NULL, "kinetic,ktz8866-slave");
> +	if (!np)
> +		return 0;
> +
> +	client = of_find_i2c_device_by_node(np);


I wrote on IRC - phandle to express the relationship between hardware -
and I do not see it implemented.

If you have devices depending on each other, you need to express it -
for links, for resource dependencies etc. phandle is for that usually.
Or OF graph. Or parent-child relationship.

You did not provide any description of the hardware in the binding, so I
really do not have any idea what is this setup thus how to represent it.
Use hardware terms, diagrams etc to explain the hardware in the bindings
commit. What are the addresses? Are there any shared resources? What
buses are devices sitting on, etc.

Best regards,
Krzysztof