Hi Shimoda-san, On Tue, Oct 18, 2016 at 8:19 AM, Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote: >> From: geert.uytterhoeven@xxxxxxxxx >> Sent: Monday, October 17, 2016 9:28 PM >> On Mon, Oct 17, 2016 at 9:10 AM, Yoshihiro Shimoda >> <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote: >> > This patch adds sysfs "otg_inputs" for usb role swap. This parameter >> > is write-only and if you use them as the following, you can swap >> > the usb role. >> >> Thank you for your patch! > > Thank you for the review! > >> > For example: >> > 1) connect a usb cable using 2 salvator-x boards >> > 2) On A-device (as host), you input the following command: >> > # echo a_bus_req/ > /sys/devices/platform/soc/ee080200.usb-phy/otg_inputs >> > 3) On B-device (as peripheral), you input the following command: >> > # echo b_bus_req > /sys/devices/platform/soc/ee080200.usb-phy/otg_inputs >> >> At first, I thought the trailing "/" was a typo... >> >> > --- /dev/null >> > +++ b/Documentation/ABI/testing/sysfs-platform-phy-rcar-gen3-usb2 >> > @@ -0,0 +1,11 @@ >> > +What: /sys/devices/platform/<phy-name>/otg-inputs >> > +Date: October 2016 >> > +KernelVersion: 4.10 >> > +Contact: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> >> > +Description: >> > + This write-only file changes the phy mode for role swap of usb. >> > + This file accepts the following strings: >> > + "a_bus_req/" - switching from A-Host to A-Peripheral >> > + "a_bus_drop" - switching from A-Peripheral to A-Host >> > + "b_bus_req" - switching from B-Peripheral to B-Host >> > + "b_bus_req/" - switching from B-Host to B-Peripheral >> >> ... until I read the above. >> >> What's the rationale of doing it like this? I.e. >> 1. Why differentiate by trailing "/"? > > This usb role swap feature is not compatible with USB OTG though, > but this strings are from the manual that usb.org released: > http://www.usb.org/developers/docs/usb20_docs/ > --> usb_20_091216.zip > --> USB OTG and Embedded Host/USB_OTG_and_EH_2-0-version 1_1a.pdf > Please refer to the following figures: > - Figure 7-1: OTG A-device with HNP State Diagram > - Figure 7-4: OTG B-device with HNP State Diagram > > So, it seems the "/" means FALSE. > >> 2. Why the asymmetry ("a_bus_drop" vs. "a_bus_req")? > > This is also related the document. > - From "a_host" to "a_suspend" state if "a_bus_req/" event happens. > - From "a_suspend" to "a_host" state if "a_bus_req" event happens. > (But the driver doesn't support it and we can use "a_bus_drop".) > - From "a_peripheral" to "a_wait_vfall" state if "a_bus_drop" event happens. Thanks for the explanation! Regardless, I think it would be good to CC the USB maintainer and mailing list on next submission. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
