linux-kernel - Re: [PATCH v16 05/14] power: reset: reboot-mode: Expose sysfs for registered reboot

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Message-ID: <0e49a6b0-276c-85b4-3ffa-39e5412db522@oss.qualcomm.com>
Date: Thu, 23 Oct 2025 21:24:01 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Cc: 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>,
        John Stultz <john.stultz@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Mukesh Ojha <mukesh.ojha@....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>,
        Srinivas Kandagatla <srini@...nel.org>
Subject: Re: [PATCH v16 05/14] power: reset: reboot-mode: Expose sysfs for
 registered reboot_modes



On 10/23/2025 8:32 PM, Bartosz Golaszewski wrote:
> On Wed, 22 Oct 2025 at 16:21, Shivendra Pratap
> <shivendra.pratap@....qualcomm.com> wrote:
>>
>>
>>
>> On 10/20/2025 1:10 PM, Bartosz Golaszewski wrote:
>>> On Fri, 17 Oct 2025 at 21:40, Shivendra Pratap
>>> <shivendra.pratap@....qualcomm.com> wrote:
>>>>
>>>>>
>>>>> If you're using devres here - at least make it obvious by adding the
>>>>> devm_ prefix to the function name and make it take an explicit struct
>>>>> device * parameter so that it's clear who owns the managed resource.
>>>>>
>>>>
>>>> sure. we can add devm_ prefix to the function name.
>>>> reboot->reboot_dev is an internal member of struct reboot_mode_driver *reboot.
>>>> The struct reboot_mode_driver *reboot is owned by the calling driver.
>>>> If we want to PASS reboot->reboot_dev to the devm_ prefixed function call, we
>>>> will need to kind of split create_reboot_mode_device into two calls - device_create
>>>> in a separate function and then call the devm_ prefix function where we add the devres_alloc.
>>>> Can you suggest a bit more on this?
>>>>
>>>
>>> Ah, ok I missed the broken logic here. Devres should only be used in
>>> devices already *attached* to a driver as all managed resources will
>>> get released on driver *detach*. What you have here may "work" by
>>> accident but that's not correct and is very fragile as soon as you
>>> have some non-standard behavior or error paths. Devres won't fly here,
>>> please just use regular allocation and free whatever you need in the
>>> corresponding release/free/whatever routine.
>>
>> Thanks, got the problem here. Was using devres to associate the reboot_mode struct
>> with the driver, so that it could be retrieved later when reboot_modes_show is called.
>>
>> When reboot_modes_show is invoked, there's no direct way to identify which reboot_mode
>> instance is tied to the current driver, as multiple drivers can register with the reboot-mode
>> framework at the same time. Without devres, will need to maintain a global list of mapping for
>> all device driver structs and their corresponding reboot_mode struct. Then reboot_modes_show
>> would have to look up the correct reboot_mode struct using the device driver's pointer.
>>
>> Hope its ok to maintain that separate logic here?
>>
> 
> Why can't you just do:
> 
> device_create(rb_class, NULL, 0, data reboot->driver_name);
> 
> Where data is whatever driver data you want to associate with the new
> class device? You can then retrieve it with dev_get_drvdata() in
> callbacks.

sure. thanks for the suggestion. That will make it much simpler.

thanks,
Shivendra