linux-kernel - Re: [PATCH v3 1/2] backlight: Add Congatec Board Controller (CGBC) backlight support

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Message-ID: <aSbzomGqb4g98ADZ@aspen.lan>
Date: Wed, 26 Nov 2025 12:33:38 +0000
From: Daniel Thompson <danielt@...nel.org>
To: petri.karhula@...atron.fi
Cc: Thomas Richard <thomas.richard@...tlin.com>, Lee Jones <lee@...nel.org>,
	Jingoo Han <jingoohan1@...il.com>, Helge Deller <deller@....de>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v3 1/2] backlight: Add Congatec Board Controller (CGBC)
 backlight support

On Tue, Nov 25, 2025 at 03:29:39PM +0000, Petri Karhula via B4 Relay wrote:
> From: Petri Karhula <petri.karhula@...atron.fi>
>
> This driver provides backlight brightness control through the Linux
> backlight subsystem. It communicates with the board controller to
> adjust LCD backlight using PWM signals. Communication is done
> through Congatec Board Controller core driver.
>
> Signed-off-by: Petri Karhula <petri.karhula@...atron.fi>
> ---
>  drivers/video/backlight/Kconfig   |  11 +++
>  drivers/video/backlight/Makefile  |   1 +
>  drivers/video/backlight/cgbc_bl.c | 177 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 189 insertions(+)


> +static int cgbc_bl_probe(struct platform_device *pdev)
> +{
> +	struct cgbc_device_data *cgbc = dev_get_drvdata(pdev->dev.parent);
> +	struct backlight_properties props = { };
> +	u8 cmd_buf[4] = { CGBC_CMD_BLT0_PWM };
> +	struct backlight_device *bl_dev;
> +	struct cgbc_bl_data *bl_data;
> +	u8 reply_buf[3];
> +	int ret;
> +
> +	bl_data = devm_kzalloc(&pdev->dev, sizeof(*bl_data), GFP_KERNEL);
> +	if (!bl_data)
> +		return -ENOMEM;
> +
> +	bl_data->dev = &pdev->dev;
> +	bl_data->cgbc = cgbc;
> +
> +	ret = cgbc_command(bl_data->cgbc, cmd_buf, sizeof(cmd_buf), reply_buf,
> +			   sizeof(reply_buf), NULL);
> +	if (ret < 0)
> +		return dev_err_probe(&pdev->dev, ret,
> +				     "Failed to read initial brightness\n");
> +
> +	/*
> +	 * Get only PWM duty factor percentage,
> +	 * ignore polarity inversion bit (bit 7)
> +	 */
> +	bl_data->current_brightness = FIELD_GET(BLT_PWM_DUTY_MASK, reply_buf[0]);

It would good to common this up with cgbc_bl_get_brightness() by
providing a helper that takes struct cgbc_bl_data * and calling it
from both places.


> +
> +	props.type = BACKLIGHT_PLATFORM;
> +	props.max_brightness = CGBC_BL_MAX_BRIGHTNESS;
> +	props.brightness = bl_data->current_brightness;

New drivers should always set props.scale .
> +

> +	bl_dev = devm_backlight_device_register(&pdev->dev, "cgbc-backlight",
> +						&pdev->dev, bl_data,
> +						&cgbc_bl_ops, &props);
> +	if (IS_ERR(bl_dev))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(bl_dev),
> +			     "Failed to register backlight device\n");
> +
> +	platform_set_drvdata(pdev, bl_data);
> +
> +	return 0;
> +}
> +
> +static struct platform_driver cgbc_bl_driver = {
> +	.driver = {
> +		.name = "cgbc-backlight",
> +	},
> +	.probe = cgbc_bl_probe,
> +};


Daniel.