Device driver .shutdown() VS .remove()

Device driver .shutdown() VS .remove()

[Luca Ceresoli]

Hello,

despite having been searching for documentation I couldn't find out the
exact and detailed difference between the .shutdown() and .remove()
calls in struct device_driver.

My best understanding follows. Any amendment or clarification would be
appreciated, and why not it might end up in improving the docs.

The different intent is kind of clear: remove() is called when the
device is disconnected or otherwise removed from the system, and also
when the driver is removed (which can only happen by unloading a kernel
module, I think). shutdown() is called during reboot and shutdown.

remove() is _not_ called during shutdown and reboot.
shutdown() is not called on device or driver removal.

Things get more blurred when trying to understand what each of the two
should do.

Definitely both must stop the device from producing any events to the
rest of the system: stop DMAs, stop anything that would trigger
interrupts etc.

remove() should also "turn off" the device, but it's probably a good
idea to do in shutdown() as well in order to not leave peripherals
unnecessarily powered while rebooting.

remove() must definitely free any allocated resources, which would be
useless in shutdown().

From the above it looks like the shutdown() actions must be a subset of
remove() actions.

How much of my understanding is correct?

Thanks.
-- 
Luca

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Re: Device driver .shutdown() VS .remove()

[jim.cromie]

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On Thu, Apr 22, 2021 at 1:37 AM Luca Ceresoli <luca@lucaceresoli.net> wrote:

> Hello,
>
> despite having been searching for documentation I couldn't find out the
> exact and detailed difference between the .shutdown() and .remove()
> calls in struct device_driver.
>
>
so, I'll start by saying I know next to nothing, but most of what you said
sounds good




> From the above it looks like the shutdown() actions must be a subset of
> remove() actions.
>
>
but subset is a bit vague.
theres 2 dimensions to think about.
lifetime -  shutdown/startup is surely the longer window, add/remove happen
within that
hierarchy - subsystems must be ready to handle add / remove

fwiw, I 'grepped' (with ack), it shows a few drivers with both functions,
many others with just remove
you could see in detail what the difference is.

$> ack '(\.remove|\.shutdown)\b' drivers/

drivers/rtc/rtc-twl.c
645: .remove = twl_rtc_remove,
646: .shutdown = twl_rtc_shutdown,

>
>

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Re: Device driver .shutdown() VS .remove()

[Luca Ceresoli]

Hi Jim,

thanks for the discussion.

On 22/04/21 20:05, jim.cromie@gmail.com wrote:
> 
> 
> On Thu, Apr 22, 2021 at 1:37 AM Luca Ceresoli <luca@lucaceresoli.net
> <mailto:luca@lucaceresoli.net>> wrote:
> 
>     Hello,
> 
>     despite having been searching for documentation I couldn't find out the
>     exact and detailed difference between the .shutdown() and .remove()
>     calls in struct device_driver.
> 
> 
> so, I'll start by saying I know next to nothing, but most of what you
> said sounds good

Good to know.

>     From the above it looks like the shutdown() actions must be a subset of
>     remove() actions.
> 
> 
> but subset is a bit vague.
> theres 2 dimensions to think about.
> lifetime -  shutdown/startup is surely the longer window, add/remove
> happen within that
> hierarchy - subsystems must be ready to handle add / remove
> 
> fwiw, I 'grepped' (with ack), it shows a few drivers with both functions,
> many others with just remove
> you could see in detail what the difference is.
> 
> $> ack '(\.remove|\.shutdown)\b' drivers/
>  
> drivers/rtc/rtc-twl.c
> 645: .remove = twl_rtc_remove,
> 646: .shutdown = twl_rtc_shutdown,

I've been looking at a few of the drivers that implement both calls, and
they either look similar or they call the shutdown function within the
remove function. This reinforces the idea that remove() should do the
same things as shutdown() plus free all kernel resources.

The only exception that I noticed happen for devices that don't have to
be completely turned off during shutdown or reboot, such as RTCs.

-- 
Luca


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