linux-kernel - Re: [RFC] of/platform: Create device link between simple-mfd and its children

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20201019065208.x5k2zpuxjfhpmhdc@pengutronix.de>
Date:   Mon, 19 Oct 2020 08:52:08 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Frank Rowand <frowand.list@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        Saravana Kannan <saravanak@...gle.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] of/platform: Create device link between simple-mfd and its
 children

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@...e.de> wrote:
> > > 'simple-mfd' usage implies there might be some kind of resource sharing
> > > between the parent device and its children.
> > 
> > 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´s firmware interface:
> 
> 	firmware: firmware {
> 		compatible = "raspberrypi,bcm2835-firmware", "simple-mfd";
> 		#address-cells = <1>;
> 		#size-cells = <1>;
> 		mboxes = <&mailbox>;
> 
> 		firmware_clocks: clocks {
> 			compatible = "raspberrypi,firmware-clocks";
> 			#clock-cells = <1>;
> 		};
> 
> 		reset: reset {
> 			compatible = "raspberrypi,firmware-reset";
> 			#reset-cells = <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 through
> 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" 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


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

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)