Author: avg
Date: Thu May 7 13:11:32 2020
New Revision: 360779
URL: https://svnweb.freebsd.org/changeset/base/360779
Log:
gpioiic_attach: fix a NULL pointer crash on hints-based systems
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
Modified:
head/sys/dev/gpio/gpioiic.c
Modified: head/sys/dev/gpio/gpioiic.c
==============================================================================
--- head/sys/dev/gpio/gpioiic.c Thu May 7 12:43:28 2020 (r360778)
+++ head/sys/dev/gpio/gpioiic.c Thu May 7 13:11:32 2020 (r360779)
@@ -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);
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