MUSB dual-role on AM335x behaving weirdly

[Bin Liu]

Hi,

On Wed, Jan 21, 2015 at 10:06 AM, Maxime Ripard
<maxime.ripard at free-electrons.com> wrote:
> Hi Felipe,
>
> I'm currently working on a custom AM335x-based board, that has a OTG
> connector wired to one of the musb controlers, and Linux 3.17
>
> This OTG connector seems to behave in a weird way when it comes to
> switching from one role to another:
>
>   - The host mode works with CONFIG_USB_MUSB_DUAL_ROLE set, only if
>     the dr_mode is set to host in the DT, and only if we plug the USB
>     device after the kernel has booted. Otherwise, even though the
>     controller seems to be set up as host in the kernel logs, it
>     doesn't work. When DR-mode is set to otg, DRVVBUS is not high
>     which surely doesn't help, but there might be some other issues.
>
>   - The gadget mode works with CONFIG_USB_MUSB_DUAL_ROLE, if dr_mode
>     is set to otg and not host (obviously), and only if we plug the
>     USB cable after the kernel has booted.
>
>   - The gadget mode works with CONFIG_USB_MUSB_GADGET, and with
>     dr_mode set to otg, even if we cold plug the device.
>
>   - As you might expect from the two first items, the runtime
>     switching from gadget to host when CONFIG_USB_MUSB_DUAL_ROLE is
>     set and dr_mode is set in otg doesn't work either.
>
> It looks like it's only waiting for an interrupt to occur to read the
> ID pin state, without reading its initial value, which would explain
> why both the host and gadget enumerate only when a device/cable is
> hotplugged, and that there's some configuration bits that differ
> whenever dr_mode changes, but I couldn't really see anything standing
> out in the driver nor the datasheet.
>
> Have you already experienced something alike with that driver?

I don't use vanilla mainline kernel very often, but I don't have such
hotplug issues with TI 3.12/14 kernels [1]. I only use
CONFIG_USB_MUSB_DUAL_ROLE though.

[1] git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git, branch
remote/origin/linux-3.14.y

Regards,
-Bin.

>
> Thanks,
> Maxime
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com