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@xxxxxxx> 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/ |
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