linux-kernel - Re: [PATCH] driver core: Call pm_runtime_put_sync() only after device

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Message-ID: <ZF3tUQFTeILXV_VT@hovoldconsulting.com>
Date:   Fri, 12 May 2023 09:40:01 +0200
From:   Johan Hovold <johan@...nel.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH] driver core: Call pm_runtime_put_sync() only after
 device_remove()

On Thu, May 11, 2023 at 04:44:25PM +0200, Rafael J. Wysocki wrote:
> On Thu, May 11, 2023 at 1:48 PM Johan Hovold <johan@...nel.org> wrote:

> > No, this seems like very bad idea and even violates the documentation
> > which clearly states that the usage counter is balanced before calling
> > remove() so that drivers can use pm_runtime_suspend() to put devices
> > into suspended state.
> 
> I missed that, sorry.
> 
> > There's is really no good reason to even try to change as this is in no
> > way a fast path.
> 
> Still, I think that while the "put" part needs to be done before
> device_remove(), the actual state change can be carried out later.
> 
> So something like
> 
>     pm_runtime_put_noidle(dev);
> 
>     device_remove(dev);
> 
>     pm_runtime_suspend(dev);
> 
> would generally work, wouldn't it?

No, as drivers typically disable runtime pm in their remove callbacks,
that pm_runtime_suspend() would amount to a no-op (and calling the
driver pm ops post unbind and the driver having freed its data would
not work either).

Johan