linux-kernel - Re: [PATCH] usb: dwc3: Support EBC feature of DWC

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Date:   Fri, 17 Nov 2023 01:51:46 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Manan Aurora <maurora@...gle.com>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "manugautam@...gle.com" <manugautam@...gle.com>,
        "badhri@...gle.com" <badhri@...gle.com>
Subject: Re: [PATCH] usb: dwc3: Support EBC feature of DWC_usb31

On Thu, Nov 16, 2023, Manan Aurora wrote:
> On Sat, Nov 11, 2023 at 4:39 AM Thinh Nguyen <Thinh.Nguyen@...opsys.com> wrote:
> >
> > On Thu, Nov 02, 2023, Manan Aurora wrote:
> > > Support configuration and use of bulk endpoints in the so-called EBC
> > > mode described in the DBC_usb31 databook (appendix E)
> > >
> > > Added a bit fifo_mode to usb_ep to indicate to the UDC driver that a
> > > specific endpoint is to operate in the EBC (or equivalent) mode when
> > > enabled
> >
> > This should be unique to dwc3, and it's only for bulk. I don't think
> > usb_ep or the user of usb_ep should know this.
> 
> In our use case we have a function driver that configures an allocated bulk
> endpoint to operate as an EBC EP. So the function driver already depends on the
> feature.

This should be abstracted from the function driver. The function driver
should not need to know about this feature.

> 
> dwc3_ep seems like the correct place to put this field but a function
> driver that allocates
> EPs and configures them for this use case would need to include dwc3 headers.
> If other vendors offer an equivalent feature this dependency would
> become an issue.
> 
> Exporting a symbol from dwc3 is an easy option but dwc3 doesn't
> currently export symbols
> hence I tried to avoid that
> 
> > Also since DWC3_DEPCFG_EBC_HWO_NOWB must be set, the controller does not
> > write back to the TRB. Did you handle how the driver would update the
> > usb request on completion? (e.g. how much was transferred).
> 
> In our use case, we intend to have a link TRB and issue a startXfer
> command. Completion
> handling and continuing the transfer will be offloaded to dedicated
> FIFO hardware.
> But we can definitely rework this to disable no-writeback mode by
> default and allow this to
> be separately enabled
> 

Ok.

Thanks,
Thinh