linux-kernel - Re: [PATCH] PM / runtime: Fixup reference counting of device link suppliers at probe

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Message-ID: <CAPDyKFphMCQ_S5aBVToGUL=Rvd0cBQ4O3Top3AYPdM79Ak_LzA@mail.gmail.com>
Date:   Fri, 18 May 2018 11:07:02 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] PM / runtime: Fixup reference counting of device link
 suppliers at probe

On 18 May 2018 at 10:58, Rafael J. Wysocki <rafael@...nel.org> wrote:
> On Fri, May 18, 2018 at 10:48 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> In the driver core, before it invokes really_probe() it runtime resumes the
>> suppliers for the device via calling pm_runtime_get_suppliers(), which also
>> increases the runtime PM usage count for each of the available supplier.
>>
>> This makes sense, as to be able to allow the consumer device to be probed
>> by its driver. However, if the driver decides to add a new supplier link
>> during ->probe(), hence updating the list of suppliers,
>
> Do any of the existing drivers do that?

Yes.

At least these, but possibly even more...

drivers/gpu/drm/rockchip/rockchip_drm_drv.c
drivers/gpu/drm/tegra/dc.c
drivers/gpu/ipu-v3/ipu-prg.c
drivers/pci/dwc/pci-dra7xx.c

>
>> the following call to pm_runtime_put_suppliers(), invoked after really_probe()
>> in the driver core, we get into trouble.

Kind regards
Uffe