linux-hardening - Re: [PATCH v2 2/3] leds: sy7802: Add support for Silergy SY7802 flash LED controller

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Date: Thu, 2 May 2024 10:10:17 +0100
From: Lee Jones <lee@...nel.org>
To: André Apitzsch <git@...tzsch.eu>
Cc: Pavel Machek <pavel@....cz>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] leds: sy7802: Add support for Silergy SY7802
 flash LED controller

On Wed, 01 May 2024, André Apitzsch wrote:

> Hi Lee Jones,
> 
> thanks for the feedback. I will address your comments in the next
> version. I have a few comments/questions though, see below.
> 
> Best regards,
> André
> 
> Am Donnerstag, dem 11.04.2024 um 13:48 +0100 schrieb Lee Jones:
> > On Mon, 01 Apr 2024, André Apitzsch via B4 Relay wrote:
> > > 
> > > [..]
> > > +
> > > +#define SY7802_TIMEOUT_DEFAULT_US	512000U
> > > +#define SY7802_TIMEOUT_MIN_US		32000U
> > > +#define SY7802_TIMEOUT_MAX_US		1024000U
> > > +#define SY7802_TIMEOUT_STEPSIZE_US	32000U
> > > +
> > > +#define SY7802_TORCH_BRIGHTNESS_MAX 8
> > > +
> > > +#define SY7802_FLASH_BRIGHTNESS_DEFAULT	14
> > > +#define SY7802_FLASH_BRIGHTNESS_MIN	0
> > > +#define SY7802_FLASH_BRIGHTNESS_MAX	15
> > > +#define SY7802_FLASH_BRIGHTNESS_STEP	1
> > 
> > Much nicer to read if everything was aligned.
> 
> Using tab size 8, SY7802_FLASH_BRIGHTNESS_* look aligned to me. Do you
> refer to SY7802_TORCH_BRIGHTNESS_MAX here? 

These were not aligned in my mailer.  You can ignore.

> > > [..]
> > > +
> > > +	/*
> > > +	 * There is only one set of flash control logic, and this
> > > flag is used to check if 'strobe'
> > 
> > The ',' before 'and' is superfluous.
> > 
> > > +	 * is currently being used.
> > > +	 */
> > 
> > Doesn't the variable name kind of imply this?
> > 
> > > +	if (chip->fled_strobe_used) {
> > > +		dev_warn(chip->dev, "Please disable strobe first
> > > [%d]\n", chip->fled_strobe_used);
> > 
> > "Cannot set torch brightness whilst strobe is enabled"
> 
> The comment and the warn message are taken from 'leds-mt6370-flash.c'.
> But I think using the warn message you suggested the comment can be
> removed.

It's an improvement, right?

> > > +		ret = -EBUSY;
> > > +		goto unlock;
> > > +	}
> > > +
> > > +	if (level)
> > > +		curr = chip->fled_torch_used | BIT(led->led_no);
> > > +	else
> > > +		curr = chip->fled_torch_used & ~BIT(led->led_no);
> > > +
> > > +	if (curr)
> > > +		val |= SY7802_MODE_TORCH;
> > > +
> > > +	/* Torch needs to be disabled first to apply new
> > > brightness */
> > 
> > "Disable touch to apply brightness"
> > 
> > > +	ret = regmap_update_bits(chip->regmap, SY7802_REG_ENABLE,
> > > SY7802_MODE_MASK,
> > > +				 SY7802_MODE_OFF);
> > > +	if (ret)
> > > +		goto unlock;
> > > +
> > > +	mask = led->led_no == SY7802_LED_JOINT ?
> > > SY7802_TORCH_CURRENT_MASK_ALL :
> > 
> > Why not just use led->led_no in place of mask?
> 
> I might be missing something, but I don't know how to use led->led_no
> in place of mask, when
> led->led_no is in {0,1,2} and
> mask is in {0x07, 0x38, 0x3f}.

This doesn't make much sense.

I guess you mean that led_no is a u8 and mask is a u32.

What happens if you cast led_no to u32 in the call to regmap_update_bits()?

> > Easier to read if you drop SY7802_TORCH_CURRENT_MASK_ALL to its own
> > line.
> > 
> > > +	       SY7802_TORCH_CURRENT_MASK(led->led_no);
> > > +
> > > [..]
> > > +
> > > +static int sy7802_probe(struct i2c_client *client)
> > > +{
> > > +	struct device *dev = &client->dev;
> > > +	struct sy7802 *chip;
> > > +	size_t count;
> > > +	int ret;
> > > +
> > > +	count = device_get_child_node_count(dev);
> > > +	if (!count || count > SY7802_MAX_LEDS)
> > > +		return dev_err_probe(dev, -EINVAL,
> > > +		       "No child node or node count over max led
> > > number %zu\n", count);
> > 
> > Split them up and report on them individually or combine the error
> > message:
> > 
> > "Invalid amount of LED nodes"
> 
> This snippet was also taken from 'leds-mt6370-flash.c'.

Old mistakes should not be repeated. :)

-- 
Lee Jones [李琼斯]