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

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Date: Thu, 02 May 2024 21:19:13 +0200
From: André Apitzsch <git@...tzsch.eu>
To: Lee Jones <lee@...nel.org>
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

Am Donnerstag, dem 02.05.2024 um 10:10 +0100 schrieb Lee Jones:
> On Wed, 01 May 2024, André Apitzsch wrote:
> 
> > > > +		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()?

Sorry, I'm still confused. Could you elaborate your original question?

> 
> > > Easier to read if you drop SY7802_TORCH_CURRENT_MASK_ALL to its
> > > own
> > > line.
> > > 
> > > > +	       SY7802_TORCH_CURRENT_MASK(led->led_no);
> > > > +
> > > > [..]
> > > > 
>