linux-kernel - Re: [PATCH v11 2/8] power: reset: reboot-mode: Add support for 64 bit magic

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Message-ID: <6227828c-5db0-41c8-956f-eea6f790ccac@lunn.ch>
Date: Sun, 20 Jul 2025 17:16:53 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Sebastian Reichel <sre@...nel.org>, Rob Herring <robh@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Souvik Chakravarty <Souvik.Chakravarty@....com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Andy Yan <andy.yan@...k-chips.com>,
	Mark Rutland <mark.rutland@....com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Konrad Dybcio <konradybcio@...nel.org>,
	cros-qcom-dts-watchers@...omium.org, Vinod Koul <vkoul@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
	Stephen Boyd <swboyd@...omium.org>,
	Andre Draszik <andre.draszik@...aro.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
	Elliot Berman <quic_eberman@...cinc.com>,
	Srinivas Kandagatla <srini@...nel.org>
Subject: Re: [PATCH v11 2/8] power: reset: reboot-mode: Add support for 64
 bit magic

On Sat, Jul 19, 2025 at 11:07:47PM +0530, Shivendra Pratap wrote:
> 
> 
> On 7/19/2025 10:27 PM, Andrew Lunn wrote:
> >>>> +static int qcom_pon_reboot_mode_write(struct reboot_mode_driver *reboot, u64 magic)
> >>>>  {
> >>>>  	struct qcom_pon *pon = container_of
> >>>>  			(reboot, struct qcom_pon, reboot_mode);
> >>>> @@ -37,7 +36,7 @@ static int qcom_pon_reboot_mode_write(struct reboot_mode_driver *reboot,
> >>>>  	ret = regmap_update_bits(pon->regmap,
> >>>>  				 pon->baseaddr + PON_SOFT_RB_SPARE,
> >>>>  				 GENMASK(7, pon->reason_shift),
> >>>> -				 magic << pon->reason_shift);
> >>>> +				 ((u32)magic) << pon->reason_shift);
> > 
> > As a general rule of thumb, code with casts is poor quality code. Try
> > to write the code without casts.
> > 
> > Maybe something like
> > 
> >       If (magic > MAX_U32)
> >       	   return -EINVAL;
> > 
> >       magic_32 = magic;
> sure will update it. And in above, should it be recommended to add a explicit
> cast(for any avoiding any compiler complains)?
>  like: magic_32 = (u32)magic;

I would hope the compiler/optimiser can figure out from the test the
line before that this is a safe conversion. So i don't think you need
a cast.

	Andrew