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Date:   Tue, 23 Mar 2021 11:08:15 +0100
From:   Robin van der Gracht <robin@protonic.nl>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Rob Herring <robh+dt@kernel.org>, Miguel Ojeda <ojeda@kernel.org>,
        Paul Burton <paulburton@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        devicetree@vger.kernel.org, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 17/17] auxdisplay: ht16k33: Add segment display LED
 support
Reply-To: robin@protonic.nl
In-Reply-To: <20210322144848.1065067-18-geert@linux-m68k.org>
References: <20210322144848.1065067-1-geert@linux-m68k.org>
 <20210322144848.1065067-18-geert@linux-m68k.org>
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On 2021-03-22 15:48, Geert Uytterhoeven wrote:
> Instantiate a single LED for a segment display.  This allows the user 
> to
> control display brightness and blinking through the LED class API and
> triggers, and exposes the display color.
> 
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> For setting display brightness, this could use the existing backlight
> support for frame buffer devices instantiated for dot-matrix displays.
> However, using the leds subsystem instead has the advantage that the
> driver can make use of the HT16K33's hardware blinking support, and can
> expose the display color.
> ---
>  drivers/auxdisplay/ht16k33.c | 81 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 77 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/auxdisplay/ht16k33.c 
> b/drivers/auxdisplay/ht16k33.c
> index 0b502a6039f89c6b..5821addd9aec5633 100644
> --- a/drivers/auxdisplay/ht16k33.c
> +++ b/drivers/auxdisplay/ht16k33.c
> @@ -29,6 +29,7 @@
>  #include <asm/unaligned.h>
> 
>  #include "line-display.h"
> +#include "../leds/leds.h"		/* for led_colors[] */
> 
>  /* Registers */
>  #define REG_SYSTEM_SETUP		0x20
> @@ -36,6 +37,10 @@
> 
>  #define REG_DISPLAY_SETUP		0x80
>  #define REG_DISPLAY_SETUP_ON		BIT(0)
> +#define REG_DISPLAY_SETUP_BLINK_OFF	(0 << 1)
> +#define REG_DISPLAY_SETUP_BLINK_2HZ	(1 << 1)
> +#define REG_DISPLAY_SETUP_BLINK_1HZ	(2 << 1)
> +#define REG_DISPLAY_SETUP_BLINK_0HZ5	(3 << 1)
> 
>  #define REG_ROWINT_SET			0xA0
>  #define REG_ROWINT_SET_INT_EN		BIT(0)
> @@ -57,6 +62,8 @@
>  #define BYTES_PER_ROW		(HT16K33_MATRIX_LED_MAX_ROWS / 8)
>  #define HT16K33_FB_SIZE		(HT16K33_MATRIX_LED_MAX_COLS * BYTES_PER_ROW)
> 
> +#define COLOR_DEFAULT		LED_COLOR_ID_RED
> +
>  enum display_type {
>  	DISP_MATRIX = 0,
>  	DISP_QUAD_7SEG,
> @@ -85,6 +92,7 @@ struct ht16k33_fbdev {
> 
>  struct ht16k33_seg {
>  	struct linedisp linedisp;
> +	struct led_classdev led;
>  	union {
>  		struct seg7_conversion_map seg7;
>  		struct seg14_conversion_map seg14;
> @@ -102,6 +110,7 @@ struct ht16k33_priv {
>  		struct ht16k33_seg seg;
>  	};
>  	enum display_type type;
> +	uint8_t blink;
>  };
> 
>  static const struct fb_fix_screeninfo ht16k33_fb_fix = {
> @@ -160,7 +169,7 @@ static DEVICE_ATTR(map_seg14, 0644, map_seg_show,
> map_seg_store);
> 
>  static int ht16k33_display_on(struct ht16k33_priv *priv)
>  {
> -	uint8_t data = REG_DISPLAY_SETUP | REG_DISPLAY_SETUP_ON;
> +	uint8_t data = REG_DISPLAY_SETUP | REG_DISPLAY_SETUP_ON | 
> priv->blink;
> 
>  	return i2c_smbus_write_byte(priv->client, data);
>  }
> @@ -175,8 +184,11 @@ static int ht16k33_brightness_set(struct
> ht16k33_priv *priv,
>  {
>  	int error;
> 
> -	if (brightness == 0)
> +	if (brightness == 0) {
> +		// Disable blink mode
> +		priv->blink = REG_DISPLAY_SETUP_BLINK_OFF;
>  		return ht16k33_display_off(priv);
> +	}
> 
>  	error = ht16k33_display_on(priv);
>  	if (error)
> @@ -186,6 +198,49 @@ static int ht16k33_brightness_set(struct
> ht16k33_priv *priv,
>  				    REG_BRIGHTNESS | (brightness - 1));
>  }
> 
> +static int ht16k33_brightness_set_blocking(struct led_classdev 
> *led_cdev,
> +					   enum led_brightness brightness)
> +{
> +	struct ht16k33_priv *priv = container_of(led_cdev, struct 
> ht16k33_priv,
> +						 seg.led);
> +
> +	return ht16k33_brightness_set(priv, brightness);
> +}
> +
> +static int ht16k33_blink_set(struct led_classdev *led_cdev,
> +			     unsigned long *delay_on, unsigned long *delay_off)
> +{
> +	struct ht16k33_priv *priv = container_of(led_cdev, struct 
> ht16k33_priv,
> +						 seg.led);
> +	unsigned int delay;
> +	uint8_t blink;
> +	int error;
> +
> +	if (!*delay_on && !*delay_off) {
> +		blink = REG_DISPLAY_SETUP_BLINK_1HZ;
> +		delay = 1000;
> +	} else if (*delay_on <= 750) {
> +		blink = REG_DISPLAY_SETUP_BLINK_2HZ;
> +		delay = 500;
> +	} else if (*delay_on <= 1500) {
> +		blink = REG_DISPLAY_SETUP_BLINK_1HZ;
> +		delay = 1000;
> +	} else {
> +		blink = REG_DISPLAY_SETUP_BLINK_0HZ5;
> +		delay = 2000;
> +	}
> +
> +	error = i2c_smbus_write_byte(priv->client,
> +				     REG_DISPLAY_SETUP | REG_DISPLAY_SETUP_ON |
> +				     blink);
> +	if (error)
> +		return error;
> +
> +	priv->blink = blink;
> +	*delay_on = *delay_off = delay;
> +	return 0;
> +}
> +
>  static void ht16k33_fb_queue(struct ht16k33_priv *priv)
>  {
>  	struct ht16k33_fbdev *fbdev = &priv->fbdev;
> @@ -578,11 +633,29 @@ static int ht16k33_fbdev_probe(struct i2c_client 
> *client,
>  static int ht16k33_seg_probe(struct i2c_client *client,
>  			     struct ht16k33_priv *priv, uint32_t brightness)
>  {
> -	struct ht16k33_seg *seg = &priv->seg;
>  	struct device *dev = &client->dev;
> +	struct device_node *node = dev->of_node;
> +	struct ht16k33_seg *seg = &priv->seg;
> +	u32 color = COLOR_DEFAULT;
>  	int err;
> 
> -	err = ht16k33_brightness_set(priv, MAX_BRIGHTNESS);
> +	of_property_read_u32(node, "color", &color);
> +	seg->led.name = devm_kasprintf(dev, GFP_KERNEL,
> +			DRIVER_NAME ":%s:" LED_FUNCTION_BACKLIGHT,
> +			color < LED_COLOR_ID_MAX ? led_colors[color] : "");
> +	seg->led.brightness_set_blocking = ht16k33_brightness_set_blocking;
> +	seg->led.blink_set = ht16k33_blink_set;
> +	seg->led.flags = LED_CORE_SUSPENDRESUME;
> +	seg->led.brightness = brightness;
> +	seg->led.max_brightness = MAX_BRIGHTNESS;
> +
> +	err = devm_led_classdev_register(dev, &seg->led);
> +	if (err) {
> +		dev_err(dev, "Failed to register LED\n");
> +		return err;
> +	}
> +
> +	err = ht16k33_brightness_set(priv, seg->led.brightness);
>  	if (err)
>  		return err;

The LED class can pretty much do what the backlight class can and more.

Maybe we can stop registering a backlight device in the fbdev case and
register a led device for both. This makes the code cleaner and drops
a dependency but will break backwards compatibility.

I'd prefer a single solution that covers both use cases, but I'm not
sure about the 'breaking backwards compatibility' consequence...

Groetjes / Kind regards,
Robin van der Gracht