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

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Message-ID: <20250128022520.6w2dovsb4rjh3qwh@synopsys.com>
Date: Tue, 28 Jan 2025 02:25:21 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        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 Wed, Jan 22, 2025, Andy Shevchenko wrote:
> On Tue, Jan 21, 2025 at 11:43:21PM +0000, Thinh Nguyen wrote:
> > On Mon, Jan 20, 2025, Andy Shevchenko wrote:
> > > On Fri, Jan 17, 2025 at 03:38:46PM +0200, Andy Shevchenko wrote:
> > > > On Thu, Jan 16, 2025 at 11:18:45PM +0000, Thinh Nguyen wrote:
> > > > > On Thu, Jan 16, 2025, Andy Shevchenko wrote:
> 
> ...
> 
> > > > > 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.
> > > 
> > > So, here is what I found:
> > > 
> > > ---8<---
> > > 
> > > However the endpoints allocated for STM and EXI debug traffic cannot be re-allocated
> > > if being used because the sideband flow control signals are hard wired to certain
> > > endpoints:
> > > • 1 High BW Bulk IN (IN#1) (RTIT)
> > > • 1 1KB BW Bulk IN (IN#8) + 1 1KB BW Bulk OUT (Run Control) (OUT#8)
> > > 
> > > In device mode, since RTIT (EP#1) and EXI/RunControl (EP#8) uses External Buffer
> > > Control (EBC) mode, these endpoints are to be mapped to EBC mode (to be done by
> > > EXI target driver). Additionally TRB for RTIT and EXI are maintained in STM (System
> > > Trace Module) unit and the EXI target driver will as well configure the TRB location for
> > > EP #1 IN and EP#8 (IN and OUT). Since STM/PTI and EXI hardware blocks manage
> > > these endpoints and interface to OTG3 controller through EBC interface, there is no
> > > need to enable any events (such as XferComplete etc) for these end points.
> > > 
> > > ---8<---
> > > 
> > > Does it help you to understand the required quirk better?
> > 
> > Thanks for looking up the info. This makes more sense now. So these
> > endpoints use EBC. Can you also provide this info to the commit?
> 
> Sure, since I published it already it makes no difference if it appears in the
> Git log (from the publicity point of view).
> 

It's more difficult to find this outside of git log, especially to a
link version of a git change that's not applied.

BR,
Thinh