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gpioiic_attach: fix a NULL pointer crash on hints-based systems

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The attach method uses GPIO_GET_BUS() to get a "newbus" device
that provides a pin.  But on hints-based systems a GPIO controller
driver might not be fully initialized yet and it does not know gpiobus
hanging off it.  Thus, GPIO_GET_BUS() cannot be called yet.
The reason is that controller drivers typically create a child gpiobus
using gpiobus_attach_bus() and that leads to the following call chain:
gpiobus_attach_bus() -> gpiobus_attach() ->
bus_generic_attach(gpiobus) -> gpioiic_attach().
So, gpioiic_attach() is called before gpiobus_attach_bus() returns.

I observed this bug with nctgpio driver on amd64.
I think that the problem was introduced in r355276.

The fix is to avoid calling GPIO_GET_BUS() from the attach method.
Instead, we know that on hints-based systems only the parent gpiobus can
provide the pins.
Nothing is changed for FDT-based systems.

MFC after:	1 week
This commit is contained in:
Andriy Gapon 2020-05-07 13:11:32 +00:00
parent e47f1857b2
commit 20077ec02c
1 changed files with 11 additions and 1 deletions
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12
sys/dev/gpio/gpioiic.c
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@ -303,10 +303,20 @@ gpioiic_attach(device_t dev)
return (ENXIO);
}
/* Say what we came up with for pin config. */
/*
* Say what we came up with for pin config.
* NB: in the !FDT case the controller driver might not be set up enough
* for GPIO_GET_BUS() to work. Also, our parent is the only gpiobus
* that can provide our pins.
*/
device_printf(dev, "SCL pin: %s:%d, SDA pin: %s:%d\n",
#ifdef FDT
device_get_nameunit(GPIO_GET_BUS(sc->sclpin->dev)), sc->sclpin->pin,
device_get_nameunit(GPIO_GET_BUS(sc->sdapin->dev)), sc->sdapin->pin);
#else
device_get_nameunit(device_get_parent(dev)), sc->sclpin->pin,
device_get_nameunit(device_get_parent(dev)), sc->sdapin->pin);
#endif
/* Add the bitbang driver as our only child; it will add iicbus. */
device_add_child(sc->dev, "iicbb", -1);