Messages in this thread |  | | From | Geert Uytterhoeven <> | Date | Mon, 17 Oct 2016 14:27:39 +0200 | Subject | Re: [PATCH] phy: rcar-gen3-usb2: add sysfs for usb role swap |
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Hi Shimoda-san,
On Mon, Oct 17, 2016 at 9:10 AM, Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com> 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!
> 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@renesas.com> > +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 "/"? 2. Why the asymmetry ("a_bus_drop" vs. "a_bus_req")?
I do not really follow USB development, so I please accepty my apologies if I missed the discussion and valid arguments that lead to this.
I did find Documentation/ABI/testing/sysfs-platform-chipidea-usb-otg, which uses similar naming, but a slightly different mechanism (multiple sysfs virtual files with 0/1 states).
Thanks!
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
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
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