Re: [PATCH v4 12/14] video: backlight: lm3533_bl: Set initial mapping mode from DT

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Sysfs show functions `show_linear` and `show_als_en` incorrectly handle the boolean return value of `regmap_test_bits()`, causing them to return early without formatting output when the bit is set.
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commit be155a9e9c191a4d2a13bb2df4a54c1332803f87
Author: Svyatoslav Ryhel <clamor95@gmail.com>

video: backlight: lm3533_bl: Set initial mapping mode from DT
    
Add support to obtain the initial mapping mode from DT instead of leaving
it unconfigured.

> diff --git a/drivers/video/backlight/lm3533_bl.c b/drivers/video/backlight/lm3533_bl.c
> index 9ad7ea1bbbccb..4f8cde9f290d0 100644
> --- a/drivers/video/backlight/lm3533_bl.c
> +++ b/drivers/video/backlight/lm3533_bl.c

[ ... ]

I noticed a regression in show_linear() and show_als_en() (modified by the
patch 'video: backlight: lm3533_bl: Improve logic of sysfs functions' in
this series) where regmap_test_bits() is called to check if a specific
bit is set:

drivers/video/backlight/lm3533_bl.c:show_als_en() {
	...
	ret = regmap_test_bits(bl->regmap, LM3533_REG_CTRLBANK_AB_BCONF,
			       CTRLBANK_AB_BCONF_ALS(ctrlbank));
	if (ret)
		return ret;

	return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
}

[Severity: High]
Does this code handle the boolean return value of regmap_test_bits()
correctly?

Since regmap_test_bits() returns 1 if the bit is set, this error check
triggers when the bit is set and returns 1 directly instead of formatting
the string.

Returning 1 from a sysfs show function signals to the sysfs core that 1 byte
was written to the buffer. Because the sysfs buffer is zero-initialized prior
to the call, doesn't this return a null byte (\0) to userspace instead of the
expected string "1\n"?

The same pattern appears in show_linear():

drivers/video/backlight/lm3533_bl.c:show_linear() {
	...
	ret = regmap_test_bits(bl->regmap, LM3533_REG_CTRLBANK_AB_BCONF,
			       CTRLBANK_AB_BCONF_MODE(ctrlbank));
	if (ret)
		return ret;

	return scnprintf(buf, PAGE_SIZE, "%x\n", ret);
}

[Severity: High]
Will this also fail to format the output string and return a null byte to
userspace when the feature is enabled?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260606045738.21050-1-clamor95@gmail.com?part=12