[Adding Olof] On Mon, Aug 12, 2013 at 10:51:36AM +0100, Mark Brown wrote: > On Sun, Aug 11, 2013 at 09:53:01PM -0400, Alan Stern wrote: > > On Sun, 11 Aug 2013, Mark Brown wrote: > > > > One example that's bugging me right now is that on the Insignal Arndale > > > platform there's a USB hub connected to one of the USB ports on the SoC > > > (not as a PHY, it seems we also need the internal PHY running to talk to > > > the device). The hub needs to be "plugged" into the SoC after the SoC > > > USB controller has started with some GPIOs so we need to tell the system > > > that the hub exists and needs to be synchronised with the USB controller. > > > On the surface, this seems like a particularly simple case. Why wait > > until the SoC's USB controller has started? Why not "plug in" the hub > > via the GPIOs right from the beginning? > > I tried that, it doesn't seem to work - for some reason it seems that > the hub is only successfully enumerated if it starts after its parent is > running. I don't know enough about USB to speculate on why that might > be, the GPIOs are brining the device out of reset not applying power or > anything. > > > > Another case that's going to be problematic once it's in mainline is > > > Slimbus - this is a bus used in some embedded audio subsystems which is > > > enumerable in a similar manner to USB but where the devices on the bus > > > are normally powered up only on demand (causing them to hotplug when > > > used and unplug when idle) and have at least interrupt lines wired to > > > the SoC using a normal interrupt outside the enumerable bus. > > > That is indeed more difficult, because it requires geniune cooperation > > between the bus and platform subsystems. > > Yeah. You might want to do the same with for example a USB network > controller when you're in flight only mode, that seems to be one of the > more common reasons for doing this sort of thing with USB. As I understand it, the wifi chip on the Snow Chromebook has a similar issue -- it hangs off of a probeable SDIO bus, but needs a regulator poked for it to turn on and become probeable (see exynos_wifi_bt_set_power in [1]). Thanks, Mark. [1] http://git.chromium.org/gitweb/?p=chromiumos/third_party/kernel.git;a=blob;f=arch/arm/mach-exynos/mach-exynos5-dt.c;h=d131241ea78b7d89df21e676e284ddfd369b4da0;hb=refs/heads/chromeos-3.4 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
