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Date:   Mon, 19 Oct 2020 08:52:08 +0200
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        Frank Rowand <frowand.list@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@lists.infradead.org>,
        Saravana Kannan <saravanak@google.com>,
        devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] of/platform: Create device link between simple-mfd and its
 children
Message-ID: <20201019065208.x5k2zpuxjfhpmhdc@pengutronix.de>
References: <20201015114346.15743-1-nsaenzjulienne@suse.de>
 <CAL_JsqLvzsdAfx56jQqPSd1r=P20C8DURKKZ9kke-L2owqr0fg@mail.gmail.com>
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On Fri, Oct 16, 2020 at 05:26:56PM +0200, Nicolas Saenz Julienne wrote:
> On Fri, 2020-10-16 at 09:38 -0500, Rob Herring wrote:
> > On Thu, Oct 15, 2020 at 6:43 AM Nicolas Saenz Julienne
> > <nsaenzjulienne@suse.de> wrote:
> > > 'simple-mfd' usage implies there might be some kind of resource shari=
ng
> > > between the parent device and its children.
> >=20
> > It does? No! The reason behind simple-mfd was specifically because
> > there was no parent driver or dependency on the parent. No doubt
> > simple-mfd has been abused.
>=20
> Fair enough, so we're doing things wrong. Just for the record, I'm lookin=
g at
> RPi=B4s firmware interface:
>=20
> 	firmware: firmware {
> 		compatible =3D "raspberrypi,bcm2835-firmware", "simple-mfd";
> 		#address-cells =3D <1>;
> 		#size-cells =3D <1>;
> 		mboxes =3D <&mailbox>;
>=20
> 		firmware_clocks: clocks {
> 			compatible =3D "raspberrypi,firmware-clocks";
> 			#clock-cells =3D <1>;
> 		};
>=20
> 		reset: reset {
> 			compatible =3D "raspberrypi,firmware-reset";
> 			#reset-cells =3D <1>;
> 		};
> 		[...]
> 	};
>=20
> Note that "raspberrypi,bcm2835-firmware" has a driver, it's not just a
> placeholder. Consumer drivers get a handle to RPi's firmware interface th=
rough
> the supplier's API, rpi_firmware_get(). The handle to firmware becomes
> meaningless if it is unbinded, which I want to protect myself against.
>=20
> A simpler solution would be to manually create a device link between both
> devices ("raspberrypi,bcm2835-firmware" and "raspberrypi,firmware-clocks"=
 for
> example) upon calling rpi_firmware_get(). But I wanted to try addressing =
the
> problem in a generic way first.

IMHO rpi_firmware_get() should get a reference on the firmware device
(and call try_module_get()) which prevents unbinding it.

Best regards
Uwe


--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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