Re: [PATCH] usb: dwc3: Support EBC feature of DWC_usb31

[Manan Aurora]

On Sat, Nov 11, 2023 at 4:39 AM Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx> 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.

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

>
> BR,
> Thinh
>
> >
> > Added macros for bits 15 and 14 of DEPCFG parameter 1 to indicate EBC
> > mode and write back behaviour. These bits will be set to 1 when
> > configuring an EBC endpoint as described in the programming guide
> >
> > Signed-off-by: Manan Aurora <maurora@xxxxxxxxxx>
> > ---
> >  drivers/usb/dwc3/core.h    | 1 +
> >  drivers/usb/dwc3/gadget.c  | 6 ++++++
> >  drivers/usb/dwc3/gadget.h  | 2 ++
> >  include/linux/usb/gadget.h | 4 ++++
> >  4 files changed, 13 insertions(+)
> >
> > diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> > index efe6caf4d0e8..c5b578188cd3 100644
> > --- a/drivers/usb/dwc3/core.h
> > +++ b/drivers/usb/dwc3/core.h
> > @@ -374,6 +374,7 @@
> >  /* Global HWPARAMS4 Register */
> >  #define DWC3_GHWPARAMS4_HIBER_SCRATCHBUFS(n) (((n) & (0x0f << 13)) >> 13)
> >  #define DWC3_MAX_HIBER_SCRATCHBUFS           15
> > +#define DWC3_EXT_BUFF_CONTROL                BIT(21)
> >
> >  /* Global HWPARAMS6 Register */
> >  #define DWC3_GHWPARAMS6_BCSUPPORT            BIT(14)
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index 858fe4c299b7..47d2737d528b 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -673,6 +673,12 @@ static int dwc3_gadget_set_ep_config(struct dwc3_ep *dep, unsigned int action)
> >               params.param1 |= DWC3_DEPCFG_BINTERVAL_M1(bInterval_m1);
> >       }
> >
> > +     if (dep->endpoint.fifo_mode) {
> > +             if (!(dwc->hwparams.hwparams4 & DWC3_EXT_BUFF_CONTROL))
> > +                     return -EINVAL;
> > +             params.param1 |= DWC3_DEPCFG_EBC_HWO_NOWB | DWC3_DEPCFG_USE_EBC;
> > +     }
> > +
> >       return dwc3_send_gadget_ep_cmd(dep, DWC3_DEPCMD_SETEPCONFIG, &params);
> >  }
> >
> > diff --git a/drivers/usb/dwc3/gadget.h b/drivers/usb/dwc3/gadget.h
> > index 55a56cf67d73..fd7a4e94397e 100644
> > --- a/drivers/usb/dwc3/gadget.h
> > +++ b/drivers/usb/dwc3/gadget.h
> > @@ -26,6 +26,8 @@ struct dwc3;
> >  #define DWC3_DEPCFG_XFER_NOT_READY_EN        BIT(10)
> >  #define DWC3_DEPCFG_FIFO_ERROR_EN    BIT(11)
> >  #define DWC3_DEPCFG_STREAM_EVENT_EN  BIT(13)
> > +#define DWC3_DEPCFG_EBC_HWO_NOWB     BIT(14)
> > +#define DWC3_DEPCFG_USE_EBC          BIT(15)
> >  #define DWC3_DEPCFG_BINTERVAL_M1(n)  (((n) & 0xff) << 16)
> >  #define DWC3_DEPCFG_STREAM_CAPABLE   BIT(24)
> >  #define DWC3_DEPCFG_EP_NUMBER(n)     (((n) & 0x1f) << 25)
> > diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
> > index 6532beb587b1..c526ae09bcee 100644
> > --- a/include/linux/usb/gadget.h
> > +++ b/include/linux/usb/gadget.h
> > @@ -209,6 +209,9 @@ struct usb_ep_caps {
> >   *   by this EP (0 - 16, actual number is 2^n)
> >   * @mult: multiplier, 'mult' value for SS Isoc EPs
> >   * @maxburst: the maximum number of bursts supported by this EP (for usb3)
> > + * @fifo_mode: indicates that the control of this EP is handed off to an
> > + *   hardware fifo device. Depends on hardware support eg. EBC feature
> > + *   of DWC usb3.1 device or equivalent. Set before enabling the EP
> >   * @driver_data:for use by the gadget driver.
> >   * @address: used to identify the endpoint when finding descriptor that
> >   *   matches connection speed
> > @@ -236,6 +239,7 @@ struct usb_ep {
> >       unsigned                max_streams:16;
> >       unsigned                mult:2;
> >       unsigned                maxburst:5;
> > +     unsigned                fifo_mode:1;
> >       u8                      address;
> >       const struct usb_endpoint_descriptor    *desc;
> >       const struct usb_ss_ep_comp_descriptor  *comp_desc;
> > --
> > 2.42.0.820.g83a721a137-goog
> >