linux-kernel - Re: [PATCH v18 2/3] leds: add basic support for TI/National Semiconductor LP5812 LED Driver

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Message-Id: <20251127145817.172871-1-trannamatk@gmail.com>
Date: Thu, 27 Nov 2025 21:58:17 +0700
From: Nam Tran <trannamatk@...il.com>
To: lee@...nel.org
Cc: gregkh@...uxfoundation.org,
	pavel@...nel.org,
	rdunlap@...radead.org,
	christophe.jaillet@...adoo.fr,
	krzk+dt@...nel.org,
	robh@...nel.org,
	conor+dt@...nel.org,
	corbet@....net,
	linux-leds@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v18 2/3] leds: add basic support for TI/National Semiconductor LP5812 LED Driver

On Thu, 27 Nov 2025, Lee Jones wrote:

> On Wed, 26 Nov 2025, Nam Tran wrote:
> 
> > On Tue, 25 Nov 2025, Lee Jones wrote:
> > 
> > > > +static ssize_t parse_drive_mode(struct lp5812_chip *chip, const char *str)
> > > > +{
> > > > +	int i;
> > > > +
> > > > +	chip->u_drive_mode.s_drive_mode.mix_sel_led_0 = false;
> > > > +	chip->u_drive_mode.s_drive_mode.mix_sel_led_1 = false;
> > > > +	chip->u_drive_mode.s_drive_mode.mix_sel_led_2 = false;
> > > > +	chip->u_drive_mode.s_drive_mode.mix_sel_led_3 = false;
> > > > +
> > > > +	if (sysfs_streq(str, LP5812_MODE_DIRECT_NAME)) {
> > > > +		chip->u_drive_mode.s_drive_mode.led_mode = LP5812_MODE_DIRECT_VALUE;
> > > > +		return 0;
> > > > +	}
> > > > +
> > > > +	for (i = 0; i < ARRAY_SIZE(chip_mode_map); i++) {
> > > > +		if (!sysfs_streq(str, chip_mode_map[i].mode_name))
> > > > +			continue;
> > > > +
> > > > +		chip->u_drive_mode.s_drive_mode.led_mode = chip_mode_map[i].mode;
> > > > +		chip->u_scan_order.s_scan_order.scan_order_0 = chip_mode_map[i].scan_order_0;
> > > > +		chip->u_scan_order.s_scan_order.scan_order_1 = chip_mode_map[i].scan_order_1;
> > > > +		chip->u_scan_order.s_scan_order.scan_order_2 = chip_mode_map[i].scan_order_2;
> > > > +		chip->u_scan_order.s_scan_order.scan_order_3 = chip_mode_map[i].scan_order_3;
> > > 
> > > Where are all of these used?
> > 
> > These fields are part of unions (u_drive_mode and u_scan_order).
> > The bitfields are packed into drive_mode_val and scan_order_val, which are
> > written to DEV_CONFIG1 and DEV_CONFIG2 in lp5812_set_drive_mode_scan_order().
> 
> Sure, but where.  What line of code?

These fields are used in lp5812_set_drive_mode_scan_order() when writing the
packed register values

	val = chip->u_drive_mode.drive_mode_val;
	ret = lp5812_write(chip, LP5812_DEV_CONFIG1, val);
	if (ret)
		return ret;

	val = chip->u_scan_order.scan_order_val;
	ret = lp5812_write(chip, LP5812_DEV_CONFIG2, val);

This is where the bitfields set in parse_drive_mode() are used.

Best regards,
Nam Tran