USB init before using usb_serial_acm gadget?

Loic Poulain loic.poulain at linaro.org
Thu Apr 14 22:15:00 CEST 2022


Hi Sergey,


On Thu, 14 Apr 2022 at 20:31, Sergey Nazaryev <sergey at coolautomation.com> wrote:
>
> Hi!
>
> As I can see, recently [1] the implementation of USB ACM gadget has
> been merged into U-boot master. I tried to use it but the problem is
> that running `setenv stdout usbacm` on my board based on STM32MP157
> leads to errors below:
>
> STM32MP> setenv stdout usbacm
> couldn't find an available UDC
> g_dnl_register: failed!, error: -19
> ## Error inserting "stdout" variable, errno=22
>
> After some research I've found that USB OTG controller must be
> initialized somehow before we can actually start using any gadget.
> For instance, on my STM32MP board `dwc2_udc_otg_probe` should be
> called. My research shows that `usb_gadget_initalize` is responsible
> for it; so, for this reason, there are explicit calls of
> `usb_gadget_initialize` (e.g. usb_dnl_dfu [2], usb_dnl_sdp [3])
> before actual usage of any gadget.
>
> However, unlike all other gadgets, usb_serial_acm code and code that
> uses it don't call usb_gadget_initialize at all. Okay, I understand
> that usb_serial_acm shouldn't initialize USB controllers by itself,
> but it's still unclear who must be responsible for it.
>
> So, my main question is: what's the best place for
> `usb_gadget_initialize` call? Should I put it to board-specific code
> (board/vendor/xxx.c) or maybe it's better to put `usb_gadget_initialize`
> into new `usb` subcommand (`usb otgstart` or something like that) and
> call it before `setenv stdout usbacm`?

Yes, you're right. I did not catch this problem because the iMX
board/platform I've tested on automatically initializes the usb
controller in the right role (peripheral) based on devicetree
property... but it's specific to that host driver.

So I think the right place to call usb_gadget_initialize is probably
before registering the acm gadget function into acm_stdio_start(). Can
you try this? and submit a follow_up fix patch if working?

Regards,
Loic


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