Re: [PATCH] backlight: Delete the OT200 backlight driver

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On Fri, Jun 26, 2020 at 12:25:00PM +0200, Linus Walleij wrote:
> This driver has no in-kernel users. The device can only be populated
> by board files since it does not support device tree nor ACPI,
> and nothing in the kernel creates a device named "ot200-backlight".
> 
> This driver has been in the kernel since 2012. If it is used by
> out-of-tree code that code should have been upstreamed by now,
> it's been 8 years.
> 
> It uses the idiomatic forked GPIO of the CS5535 which combines
> pin control and GPIO into its private custom interface, which
> causes me a headache because that is not how we do things these
> days: we creates separate pin control and GPIO drivers.
> 
> Delete this unused driver.
> 
> Cc: Christian Gmeiner <christian.gmeiner@xxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

I was curious about this if only because this a driver for an
x86 system and I wondered how the platform device could ever
have been registered.

However I drew a total blank... I can find some tweaks to
coreboot that make this code work better[1] but even after
a careful search of the coreboot code (just in case some
driver I don't know about managed to fetch the
"ot200-backlight" string from the firmware) but I can't find
any code within reach of a search engine (out of tree of not)
that could cause this driver to activate :-(

So, unless we get objections, I've reached the same view
as Linus (and in this post have documented the effort involved):
Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>


Daniel.

[1]
https://review.coreboot.org/cgit/coreboot.git/commit/?id=4412bc4

> ---
>  drivers/video/backlight/Kconfig    |   7 --
>  drivers/video/backlight/Makefile   |   1 -
>  drivers/video/backlight/ot200_bl.c | 162 -----------------------------
>  3 files changed, 170 deletions(-)
>  delete mode 100644 drivers/video/backlight/ot200_bl.c
> 
> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> index 7d22d7377606..95c546cc8774 100644
> --- a/drivers/video/backlight/Kconfig
> +++ b/drivers/video/backlight/Kconfig
> @@ -386,13 +386,6 @@ config BACKLIGHT_LP8788
>  	help
>  	  This supports TI LP8788 backlight driver.
>  
> -config BACKLIGHT_OT200
> -	tristate "Backlight driver for ot200 visualisation device"
> -	depends on CS5535_MFGPT && GPIO_CS5535
> -	help
> -	  To compile this driver as a module, choose M here: the module will be
> -	  called ot200_bl.
> -
>  config BACKLIGHT_PANDORA
>  	tristate "Backlight driver for Pandora console"
>  	depends on TWL4030_CORE
> diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
> index 0c1a1524627a..2072d21b60f7 100644
> --- a/drivers/video/backlight/Makefile
> +++ b/drivers/video/backlight/Makefile
> @@ -45,7 +45,6 @@ obj-$(CONFIG_BACKLIGHT_LP8788)		+= lp8788_bl.o
>  obj-$(CONFIG_BACKLIGHT_LV5207LP)	+= lv5207lp.o
>  obj-$(CONFIG_BACKLIGHT_MAX8925)		+= max8925_bl.o
>  obj-$(CONFIG_BACKLIGHT_OMAP1)		+= omap1_bl.o
> -obj-$(CONFIG_BACKLIGHT_OT200)		+= ot200_bl.o
>  obj-$(CONFIG_BACKLIGHT_PANDORA)		+= pandora_bl.o
>  obj-$(CONFIG_BACKLIGHT_PCF50633)	+= pcf50633-backlight.o
>  obj-$(CONFIG_BACKLIGHT_PWM)		+= pwm_bl.o
> diff --git a/drivers/video/backlight/ot200_bl.c b/drivers/video/backlight/ot200_bl.c
> deleted file mode 100644
> index 23ee7106c72a..000000000000
> --- a/drivers/video/backlight/ot200_bl.c
> +++ /dev/null
> @@ -1,162 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-only
> -/*
> - * Copyright (C) 2012 Bachmann electronic GmbH
> - *	Christian Gmeiner <christian.gmeiner@xxxxxxxxx>
> - *
> - * Backlight driver for ot200 visualisation device from
> - * Bachmann electronic GmbH.
> - */
> -
> -#include <linux/module.h>
> -#include <linux/fb.h>
> -#include <linux/backlight.h>
> -#include <linux/gpio.h>
> -#include <linux/platform_device.h>
> -#include <linux/cs5535.h>
> -
> -static struct cs5535_mfgpt_timer *pwm_timer;
> -
> -/* this array defines the mapping of brightness in % to pwm frequency */
> -static const u8 dim_table[101] = {0, 0, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2,
> -				  2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4,
> -				  4, 5, 5, 5, 5, 6, 6, 6, 7, 7, 7, 8, 8, 9, 9,
> -				  10, 10, 11, 11, 12, 12, 13, 14, 15, 15, 16,
> -				  17, 18, 19, 20, 21, 22, 23, 24, 26, 27, 28,
> -				  30, 31, 33, 35, 37, 39, 41, 43, 45, 47, 50,
> -				  53, 55, 58, 61, 65, 68, 72, 75, 79, 84, 88,
> -				  93, 97, 103, 108, 114, 120, 126, 133, 140,
> -				  147, 155, 163};
> -
> -struct ot200_backlight_data {
> -	int current_brightness;
> -};
> -
> -#define GPIO_DIMM	27
> -#define SCALE		1
> -#define CMP1MODE	0x2	/* compare on GE; output high on compare
> -				 * greater than or equal */
> -#define PWM_SETUP	(SCALE | CMP1MODE << 6 | MFGPT_SETUP_CNTEN)
> -#define MAX_COMP2	163
> -
> -static int ot200_backlight_update_status(struct backlight_device *bl)
> -{
> -	struct ot200_backlight_data *data = bl_get_data(bl);
> -	int brightness = bl->props.brightness;
> -
> -	if (bl->props.state & BL_CORE_FBBLANK)
> -		brightness = 0;
> -
> -	/* enable or disable PWM timer */
> -	if (brightness == 0)
> -		cs5535_mfgpt_write(pwm_timer, MFGPT_REG_SETUP, 0);
> -	else if (data->current_brightness == 0) {
> -		cs5535_mfgpt_write(pwm_timer, MFGPT_REG_COUNTER, 0);
> -		cs5535_mfgpt_write(pwm_timer, MFGPT_REG_SETUP,
> -			MFGPT_SETUP_CNTEN);
> -	}
> -
> -	/* apply new brightness value */
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_CMP1,
> -		MAX_COMP2 - dim_table[brightness]);
> -	data->current_brightness = brightness;
> -
> -	return 0;
> -}
> -
> -static int ot200_backlight_get_brightness(struct backlight_device *bl)
> -{
> -	struct ot200_backlight_data *data = bl_get_data(bl);
> -	return data->current_brightness;
> -}
> -
> -static const struct backlight_ops ot200_backlight_ops = {
> -	.update_status	= ot200_backlight_update_status,
> -	.get_brightness	= ot200_backlight_get_brightness,
> -};
> -
> -static int ot200_backlight_probe(struct platform_device *pdev)
> -{
> -	struct backlight_device *bl;
> -	struct ot200_backlight_data *data;
> -	struct backlight_properties props;
> -	int retval = 0;
> -
> -	/* request gpio */
> -	if (devm_gpio_request(&pdev->dev, GPIO_DIMM,
> -				"ot200 backlight dimmer") < 0) {
> -		dev_err(&pdev->dev, "failed to request GPIO %d\n", GPIO_DIMM);
> -		return -ENODEV;
> -	}
> -
> -	/* request timer */
> -	pwm_timer = cs5535_mfgpt_alloc_timer(7, MFGPT_DOMAIN_ANY);
> -	if (!pwm_timer) {
> -		dev_err(&pdev->dev, "MFGPT 7 not available\n");
> -		return -ENODEV;
> -	}
> -
> -	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
> -	if (!data) {
> -		retval = -ENOMEM;
> -		goto error_devm_kzalloc;
> -	}
> -
> -	/* setup gpio */
> -	cs5535_gpio_set(GPIO_DIMM, GPIO_OUTPUT_ENABLE);
> -	cs5535_gpio_set(GPIO_DIMM, GPIO_OUTPUT_AUX1);
> -
> -	/* setup timer */
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_CMP1, 0);
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_CMP2, MAX_COMP2);
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_SETUP, PWM_SETUP);
> -
> -	data->current_brightness = 100;
> -	props.max_brightness = 100;
> -	props.brightness = 100;
> -	props.type = BACKLIGHT_RAW;
> -
> -	bl = devm_backlight_device_register(&pdev->dev, dev_name(&pdev->dev),
> -					&pdev->dev, data, &ot200_backlight_ops,
> -					&props);
> -	if (IS_ERR(bl)) {
> -		dev_err(&pdev->dev, "failed to register backlight\n");
> -		retval = PTR_ERR(bl);
> -		goto error_devm_kzalloc;
> -	}
> -
> -	platform_set_drvdata(pdev, bl);
> -
> -	return 0;
> -
> -error_devm_kzalloc:
> -	cs5535_mfgpt_free_timer(pwm_timer);
> -	return retval;
> -}
> -
> -static int ot200_backlight_remove(struct platform_device *pdev)
> -{
> -	/* on module unload set brightness to 100% */
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_COUNTER, 0);
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_SETUP, MFGPT_SETUP_CNTEN);
> -	cs5535_mfgpt_write(pwm_timer, MFGPT_REG_CMP1,
> -		MAX_COMP2 - dim_table[100]);
> -
> -	cs5535_mfgpt_free_timer(pwm_timer);
> -
> -	return 0;
> -}
> -
> -static struct platform_driver ot200_backlight_driver = {
> -	.driver		= {
> -		.name	= "ot200-backlight",
> -	},
> -	.probe		= ot200_backlight_probe,
> -	.remove		= ot200_backlight_remove,
> -};
> -
> -module_platform_driver(ot200_backlight_driver);
> -
> -MODULE_DESCRIPTION("backlight driver for ot200 visualisation device");
> -MODULE_AUTHOR("Christian Gmeiner <christian.gmeiner@xxxxxxxxx>");
> -MODULE_LICENSE("GPL");
> -MODULE_ALIAS("platform:ot200-backlight");
> -- 
> 2.25.4
> 
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