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

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Message-ID: <CACMJSetctEH4K58R9JvSYNzzYgE0NGMsAr5JxiZ4RH_3T08x-A@mail.gmail.com>
Date: Thu, 23 Oct 2025 17:02:41 +0200
From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
To: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
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 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.

Bartosz