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Message-ID: <0f0b7021e85a832afd42c6f9016158d6d8b0b28b.camel@suse.de>
Subject: Re: [RFC] of/platform: Create device link between simple-mfd and
 its children
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Rob Herring <robh+dt@kernel.org>
Cc:     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>,
        Uwe =?ISO-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>, devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date:   Fri, 16 Oct 2020 17:26:56 +0200
In-Reply-To: <CAL_JsqLvzsdAfx56jQqPSd1r=P20C8DURKKZ9kke-L2owqr0fg@mail.gmail.com>
References: <20201015114346.15743-1-nsaenzjulienne@suse.de>
         <CAL_JsqLvzsdAfx56jQqPSd1r=P20C8DURKKZ9kke-L2owqr0fg@mail.gmail.com>
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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 sharing
> > 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.

Fair enough, so we're doing things wrong. Just for the record, I'm looking =
at
RPi=C2=B4s firmware interface:

	firmware: firmware {
		compatible =3D "raspberrypi,bcm2835-firmware", "simple-mfd";
		#address-cells =3D <1>;
		#size-cells =3D <1>;
		mboxes =3D <&mailbox>;

		firmware_clocks: clocks {
			compatible =3D "raspberrypi,firmware-clocks";
			#clock-cells =3D <1>;
		};

		reset: reset {
			compatible =3D "raspberrypi,firmware-reset";
			#reset-cells =3D <1>;
		};
		[...]
	};

Note that "raspberrypi,bcm2835-firmware" has a driver, it's not just a
placeholder. Consumer drivers get a handle to RPi's firmware interface thro=
ugh
the supplier's API, rpi_firmware_get(). The handle to firmware becomes
meaningless if it is unbinded, which I want to protect myself against.

A simpler solution would be to manually create a device link between both
devices ("raspberrypi,bcm2835-firmware" and "raspberrypi,firmware-clocks" f=
or
example) upon calling rpi_firmware_get(). But I wanted to try addressing th=
e
problem in a generic way first.

Regards,
Nicolas


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