On Tue, Dec 15, 2015 at 09:21:09PM +0100, Ulf Hansson wrote: > On 9 December 2015 at 09:55, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Wednesday 09 December 2015 16:12:24 Peter Chen wrote: > >> On Tue, Dec 08, 2015 at 09:24:03PM -0600, Rob Herring wrote: > >> > On Tue, Dec 08, 2015 at 10:58:48AM +0100, Arnd Bergmann wrote: > >> > > On Tuesday 08 December 2015 10:50:49 Philipp Zabel wrote: > >> > > > This something we don't have to define ad-hoc. The hub hangs off an USB > >> > > > controller, right? The "Open Firmware recommended practice: USB" > >> > > > document already describes how to represent USB devices in a generic > >> > > > manner: > >> > > > http://www.firmware.org/1275/bindings/usb/usb-1_0.ps > >> > > > > >> > > > Is there a reason not to reuse this? > >> > > > > >> > > > The usb hub node would be a child of the usb controller node, and it > >> > > > could use > >> > > > compatible = "usb,class9"; /* bDeviceClass 9 (Hub) */ > >> > > > >> > > Good point, I had not thought of that when I looked at the patches. > >> > > > >> > > Yes, let's do this way. I don't know if we ever implemented the simple > >> > > patch to associate a USB device with a device_node, but if not, then > >> > > let's do it now for this driver. A lot of people have asked for it in > >> > > the past. > >> > > >> > Agreed. Also, some hubs have I2C buses as well, but I still think under > >> > the USB bus is the right place. > >> > > >> > However, one complication here is often (probably this case) these > >> > addtional signals need to be controlled before the device enumerates. > >> > > >> > >> Yes, I did not find a way to let the USB bus code handle it, so I had to > >> write a platform driver to do it > > > > Looping in Ulf, he solved the same problem for SDIO devices recently, > > and probably remembers the details best. > > > > Thanks Arnd! > > Yes, that was a kind of a long outstanding issue we have had for SDIO devices. > > Several generic attempts was made to have a framework/library > available to support so called "power sequences" for exactly the same > reasons as above. > Others and myself failed to get those attempts accepted. > > Instead, I invented a mmc subsystem specific DT based solution, the > "mmc-pwrseq". > > DT documentation: > Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt > Documentation/devicetree/bindings/mmc/mmc.txt > > Long story short: The mmc host device may contain a phandle to a > mmc-pwrseq, which will describe the resources needed to power on/off > the SDIO card. > > The code is available at: > drivers/mmc/core/pwrseq* > > We didn't implement this as platform driver, but that was mostly > because I initially wanted things to be simple. Although, nothing > prevents us from converting to this as a follow up, which would make > the solution a bit less "hacky". > Thanks for your information, Ulf. -- Best Regards, Peter Chen -- 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
