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

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Message-ID: <20240507084052.GW1227636@google.com>
Date: Tue, 7 May 2024 09:40:52 +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 Sat, 04 May 2024, André Apitzsch wrote:

> Am Freitag, dem 03.05.2024 um 08:19 +0100 schrieb Lee Jones:
> > On Thu, 11 Apr 2024, Lee Jones wrote:
> > 
> > > On Mon, 01 Apr 2024, André Apitzsch via B4 Relay wrote:
> > > 
> > > > From: André Apitzsch <git@...tzsch.eu>
> > > > 
> > > > Add support for SY7802 flash LED controller. It can support up to
> > > > 1.8A
> > > > flash current.
> > > 
> > > This is a very small commit message for a 500+ line change!
> > > 
> > > Please, tell us more.
> > > 
> > > > Signed-off-by: André Apitzsch <git@...tzsch.eu>
> > > > ---
> > > >  drivers/leds/flash/Kconfig       |  11 +
> > > >  drivers/leds/flash/Makefile      |   1 +
> > > >  drivers/leds/flash/leds-sy7802.c | 532
> > > > +++++++++++++++++++++++++++++++++++++++
> > > >  3 files changed, 544 insertions(+)
> > > > 
> > > > diff --git a/drivers/leds/flash/Kconfig
> > > > b/drivers/leds/flash/Kconfig
> > > > index 809b6d98bb3e..f39f0bfe6eef 100644
> > > > --- a/drivers/leds/flash/Kconfig
> > > > +++ b/drivers/leds/flash/Kconfig
> > > > @@ -121,4 +121,15 @@ config LEDS_SGM3140
> > > >  	  This option enables support for the SGM3140 500mA
> > > > Buck/Boost Charge
> > > >  	  Pump LED Driver.
> > > >  
> > > > +config LEDS_SY7802
> > > > +	tristate "LED support for the Silergy SY7802"
> > > > +	depends on I2C && OF
> > > > +	depends on GPIOLIB
> > > > +	select REGMAP_I2C
> > > > +	help
> > > > +	  This option enables support for the SY7802 flash LED
> > > > controller.
> > > > +	  SY7802 includes torch and flash functions with
> > > > programmable current.
> > > > +
> > > > +	  This driver can be built as a module, it will be
> > > > called "leds-sy7802".
> > > > +
> > > >  endif # LEDS_CLASS_FLASH
> > > > diff --git a/drivers/leds/flash/Makefile
> > > > b/drivers/leds/flash/Makefile
> > > > index 91d60a4b7952..48860eeced79 100644
> > > > --- a/drivers/leds/flash/Makefile
> > > > +++ b/drivers/leds/flash/Makefile
> > > > @@ -11,3 +11,4 @@ obj-$(CONFIG_LEDS_QCOM_FLASH)	+= leds-qcom-
> > > > flash.o
> > > >  obj-$(CONFIG_LEDS_RT4505)	+= leds-rt4505.o
> > > >  obj-$(CONFIG_LEDS_RT8515)	+= leds-rt8515.o
> > > >  obj-$(CONFIG_LEDS_SGM3140)	+= leds-sgm3140.o
> > > > +obj-$(CONFIG_LEDS_SY7802)	+= leds-sy7802.o
> > > > diff --git a/drivers/leds/flash/leds-sy7802.c
> > > > b/drivers/leds/flash/leds-sy7802.c
> > > > new file mode 100644
> > > > index 000000000000..c03a571b0e08
> > > > --- /dev/null
> > > > +++ b/drivers/leds/flash/leds-sy7802.c
> > > > @@ -0,0 +1,532 @@
> > 
> > [...]
> > 
> > > > +static int sy7802_torch_brightness_set(struct led_classdev
> > > > *lcdev, enum led_brightness level)
> > > 
> > > s/level/brightness/
> > > 
> > > > +{
> > > > +	struct sy7802_led *led = container_of(lcdev, struct
> > > > sy7802_led, flash.led_cdev);
> > > > +	u32 led_enable_mask = led->led_no == SY7802_LED_JOINT ?
> > > > SY7802_LEDS_MASK_ALL :
> > > > +			      SY7802_LEDS_MASK(led->led_no);
> > > 
> > > Do all of the fancy multi-line assignment outside of the
> > > declaration block.
> > > 
> > > > +	u32 enable_mask = SY7802_MODE_MASK | led_enable_mask;
> > > > +	u32 val = level ? led_enable_mask : SY7802_MODE_OFF;
> > > > +	struct sy7802 *chip = led->chip;
> > > > +	u32 curr;
> > > 
> > > This is a temporary placeholder for fled_torch_used, right?
> > > 
> > > fled_torch_used_tmp?  Sometimes abbreviated to tmp.
> > > 
> > > > +	u32 mask;
> > > 
> > > That's a lot of masks.  Which one is this?
> > > 
> > > > +	int ret;
> > > > +
> > > > +	mutex_lock(&chip->mutex);
> > > > +
> > > > +	/*
> > > > +	 * 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"
> > > 
> > > > +		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?
> > 
> > mask and led->led_no are assigned the same value from this point on.
> 
> Thanks for the clarification.
> How to you come to the conclusion that mask and led->led_no are
> assigned the same value from this point on?

Because I am blind and didn't see the double equals ("==").

#shouldhavegonetospecsavers

-- 
Lee Jones [李琼斯]