linux-kernel - Re: [PATCH v1 0/3] usb: dwc3: Avoid using reserved EPs

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Message-ID: <Z4pdZZhR6m1LB3yk@smile.fi.intel.com>
Date: Fri, 17 Jan 2025 15:38:45 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...nel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Ferry Toth <fntoth@...il.com>
Subject: Re: [PATCH v1 0/3] usb: dwc3: Avoid using reserved EPs

On Thu, Jan 16, 2025 at 11:18:45PM +0000, Thinh Nguyen wrote:
> On Thu, Jan 16, 2025, Andy Shevchenko wrote:
> > On some platforms (Intel-based and AFAIK ARM-based) the EPs in the gadget
> > (USB Device Controller mode) may be reserved for some special means, such as
> > tracing. This series extends DT schema and driver to avoid using those.
> > Without this the USB gadget mode won't work properly (those devices that
> > "luckily" allocated the reserved EPs).
> > 
> > Ferry already tested the privately sent PoC of this, but I ask him again to
> > re-test this version which is slightly different.

...

> I'm not entirely clear on the reason for this change yet.
> 
> How would this even work without dwc3 managing these endpoints (all the
> init/teardown/fifo allocation/start/stop flow).

You perhaps know much better how it can be done, I have access to a limited
documentation and in practice if those endpoints are not skipped any gadget
that allocates them simply won't work, and IIRC the entire USB transfers are
stuck.

> Can you provide more info on this hardware?

I am afraid I can't provide more, sorry. I can look for some specifics,
but I'm not that guy who know anything about in-SoC tracing.

-- 
With Best Regards,
Andy Shevchenko