linux-kernel - Re: [PATCH v17 03/12] power: reset: reboot-mode: Add support for 64 bit magic

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Message-ID: <681a72ba-d8fb-bfc2-d2bb-d80ac667bc5c@oss.qualcomm.com>
Date: Mon, 10 Nov 2025 23:22:40 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Mukesh Ojha <mukesh.ojha@....qualcomm.com>
Cc: Bartosz Golaszewski <bartosz.golaszewski@...aro.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>,
        Moritz Fischer <moritz.fischer@...us.com>,
        John Stultz <john.stultz@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Andre Draszik
 <andre.draszik@...aro.org>,
        Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>,
        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>,
        Xin Liu <xin.liu@....qualcomm.com>,
        Srinivas Kandagatla <srini@...nel.org>,
        Umang Chheda <umang.chheda@....qualcomm.com>,
        Nirmesh Kumar Singh <nirmesh.singh@....qualcomm.com>
Subject: Re: [PATCH v17 03/12] power: reset: reboot-mode: Add support for 64
 bit magic



On 11/10/2025 10:00 PM, Bjorn Andersson wrote:
> On Mon, Nov 10, 2025 at 07:15:29PM +0530, Mukesh Ojha wrote:
>> On Sun, Nov 09, 2025 at 08:07:16PM +0530, Shivendra Pratap wrote:
>>> Current reboot-mode supports a single 32-bit argument for any
>>> supported mode. Some reboot-mode based drivers may require
>>> passing two independent 32-bit arguments during a reboot
>>> sequence, for uses-cases, where a mode requires an additional
>>> argument. Such drivers may not be able to use the reboot-mode
>>> driver. For example, ARM PSCI vendor-specific resets, need two
>>> arguments for its operation – reset_type and cookie, to complete
>>> the reset operation. If a driver wants to implement this
>>> firmware-based reset, it cannot use reboot-mode framework.
>>>
>>> Introduce 64-bit magic values in reboot-mode driver to
>>> accommodate dual 32-bit arguments when specified via device tree.
>>> In cases, where no second argument is passed from device tree,
>>> keep the upper 32-bit of magic un-changed(0) to maintain backward
>>> compatibility.
>>>
>>> Update the current drivers using reboot-mode for a 64-bit magic
>>> value.

[SNIP..]

>>> +	if (magic > U32_MAX)
>>> +		return -EINVAL;
>>> +
>>> +	magic_32 = magic;
>>> +
>>>  	syscon_rbm = container_of(reboot, struct syscon_reboot_mode, reboot);
>>>  
>>>  	ret = regmap_update_bits(syscon_rbm->map, syscon_rbm->offset,
>>> -				 syscon_rbm->mask, magic);
>>> +				 syscon_rbm->mask, magic_32);
> 
> As above, if we're no longer silently discarding bits, I think we should
> compare the magic against syscon_rbm->mask.
> 
> No need for a local variable, just type cast after checking the validity.

Trying to summarize below why we added these check-

the patch in v11 used typecasting and did not have any of these checks(link below):
https://lore.kernel.org/all/20250717-arm-psci-system_reset2-vendor-reboots-v11-2-df3e2b2183c3@oss.qualcomm.com/

As per below upstream review, type cast was removed and bound checks were added all-over patchset:
"As a general rule of thumb, code with casts is poor quality code. Try
to write the code without casts." - 
https://lore.kernel.org/all/8d4a42b6-657f-4c30-8e25-4213d8d53a89@lunn.ch/

We can revert to the typecast way. Please suggest.

thanks,
Shivendra