linux-kernel - Re: [PATCH v4 2/3] backlight: dwi_bl: Add Apple DWI backlight driver

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Message-ID: <Z35Y9rzS6tLVgsRo@aspen.lan>
Date: Wed, 8 Jan 2025 10:52:38 +0000
From: Daniel Thompson <danielt@...nel.org>
To: Nick Chan <towinchenmi@...il.com>
Cc: Lee Jones <lee@...nel.org>, Jingoo Han <jingoohan1@...il.com>,
	Pavel Machek <pavel@....cz>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Helge Deller <deller@....de>,
	Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
	Alyssa Rosenzweig <alyssa@...enzweig.io>,
	dri-devel@...ts.freedesktop.org, linux-leds@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, asahi@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 2/3] backlight: dwi_bl: Add Apple DWI backlight driver

On Wed, Dec 11, 2024 at 07:34:38PM +0800, Nick Chan wrote:
> Add driver for backlight controllers attached via Apple DWI 2-wire
> interface, which is found on some Apple iPhones, iPads and iPod touches
> with a LCD display.
>
> Although there is an existing apple_bl driver, it is for backlight
> controllers on Intel Macs attached via PCI, which is completely different
> from the Samsung-derived DWI block.
>
> Signed-off-by: Nick Chan <towinchenmi@...il.com>
> ---
>  drivers/video/backlight/Kconfig  |  12 +++
>  drivers/video/backlight/Makefile |   1 +
>  drivers/video/backlight/dwi_bl.c | 122 +++++++++++++++++++++++++++++++

I'd rather this was called apple_dwi_bl.c to match that config options,
etc.

> diff --git a/drivers/video/backlight/dwi_bl.c b/drivers/video/backlight/dwi_bl.c
> new file mode 100644
> index 000000000000..59e5cad0fbd8
> --- /dev/null
> +++ b/drivers/video/backlight/dwi_bl.c
> @@ -0,0 +1,122 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +/*
> + * Driver for backlight controllers attached via Apple DWI 2-wire interface
> + *
> + * Copyright (c) 2024 Nick Chan <towinchenmi@...il.com>
> + */
> +
> +#include <linux/backlight.h>
> +#include <linux/bitfield.h>
> +#include <linux/device.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +
> +#define DWI_BL_CTL			0x0
> +#define DWI_BL_CTL_SEND1		BIT(0)
> +#define DWI_BL_CTL_SEND2		BIT(4)
> +#define DWI_BL_CTL_SEND3		BIT(5)
> +#define DWI_BL_CTL_LE_DATA		BIT(6)
> +/* Only used on Apple A9 and later */
> +#define DWI_BL_CTL_SEND4		BIT(12)
> +
> +#define DWI_BL_CMD			0x4
> +#define DWI_BL_CMD_TYPE			GENMASK(31, 28)
> +#define DWI_BL_CMD_TYPE_SET_BRIGHTNESS	0xa
> +#define DWI_BL_CMD_DATA			GENMASK(10, 0)
> +
> +#define DWI_BL_CTL_SEND			(DWI_BL_CTL_SEND1 | \
> +					 DWI_BL_CTL_SEND2 | \
> +					 DWI_BL_CTL_SEND3 | \
> +					 DWI_BL_CTL_LE_DATA | \
> +					 DWI_BL_CTL_SEND4)
> +
> +#define DWI_BL_MAX_BRIGHTNESS		2047
> +
> +struct apple_dwi_bl {
> +	void __iomem *base;
> +};
> +
> +static int dwi_bl_update_status(struct backlight_device *bl)
> +{
> +	struct apple_dwi_bl *dwi_bl = bl_get_data(bl);
> +
> +	int brightness = backlight_get_brightness(bl);
> +
> +	u32 cmd = 0;
> +
> +	cmd |= FIELD_PREP(DWI_BL_CMD_DATA, brightness);
> +	cmd |= FIELD_PREP(DWI_BL_CMD_TYPE, DWI_BL_CMD_TYPE_SET_BRIGHTNESS);
> +
> +	writel(cmd, dwi_bl->base + DWI_BL_CMD);
> +	writel(DWI_BL_CTL_SEND, dwi_bl->base + DWI_BL_CTL);
> +
> +	return 0;
> +}
> +
> +static int dwi_bl_get_brightness(struct backlight_device *bl)
> +{
> +	struct apple_dwi_bl *dwi_bl = bl_get_data(bl);
> +
> +	u32 cmd = readl(dwi_bl->base + DWI_BL_CMD);
> +
> +	return FIELD_GET(DWI_BL_CMD_DATA, cmd);
> +}
> +
> +static const struct backlight_ops dwi_bl_ops = {
> +	.options = BL_CORE_SUSPENDRESUME,
> +	.get_brightness = dwi_bl_get_brightness,
> +	.update_status	= dwi_bl_update_status
> +};
> +
> +static int dwi_bl_probe(struct platform_device *dev)
> +{
> +	struct apple_dwi_bl *dwi_bl;
> +	struct backlight_device *bl;
> +	struct backlight_properties props;
> +	struct resource *res;
> +
> +	dwi_bl = devm_kzalloc(&dev->dev, sizeof(*dwi_bl), GFP_KERNEL);
> +	if (!dwi_bl)
> +		return -ENOMEM;
> +
> +	dwi_bl->base = devm_platform_get_and_ioremap_resource(dev, 0, &res);
> +	if (IS_ERR(dwi_bl->base))
> +		return PTR_ERR(dwi_bl->base);
> +
> +	memset(&props, 0, sizeof(struct backlight_properties));
> +	props.type = BACKLIGHT_RAW;
> +	props.max_brightness = DWI_BL_MAX_BRIGHTNESS;

There should be something to indicate whether the backlight controls are
linear or logarithmic here.


> +static struct platform_driver dwi_bl_driver = {
> +	.driver		= {
> +		.name	= "dwi-bl",

Again, I'd rather see apple here too (although, to be clear, I'm
perfectly happy with all the static functions and variables being
prefixed only with dwi_bl).


Daniel.