Re: [PATCH] usb: dwc3: gadget: Fix TX FIFO size for HS ISOC endpoints

From: Thinh Nguyen
Date: Wed Aug 28 2024 - 19:46:34 EST


On Wed, Aug 28, 2024, AKASH KUMAR wrote:
> Hi Thinh,
>
> On 8/28/2024 4:45 AM, Thinh Nguyen wrote:
> > On Tue, Aug 27, 2024, Akash Kumar wrote:
> > > Use 2K TX FIFO size for low-resolution UVC cameras to support the
> > > maximum possible UVC instances. Restrict 2K TX FIFO size based on
> > > the minimum maxburst required to run low-resolution UVC cameras.
> > >
> > > Signed-off-by: Akash Kumar <quic_akakum@xxxxxxxxxxx>
> > > ---
> > > drivers/usb/dwc3/gadget.c | 4 ++++
> > > 1 file changed, 4 insertions(+)
> > >
> > > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > > index 89fc690fdf34..f342ccda6705 100644
> > > --- a/drivers/usb/dwc3/gadget.c
> > > +++ b/drivers/usb/dwc3/gadget.c
> > > @@ -788,6 +788,10 @@ static int dwc3_gadget_resize_tx_fifos(struct dwc3_ep *dep)
> > > usb_endpoint_xfer_isoc(dep->endpoint.desc)) && DWC3_IP_IS(DWC31))
> > > num_fifos = dwc->tx_fifo_resize_max_num;
> > > + if (dep->endpoint.maxburst <= 1 &&
> > > + usb_endpoint_xfer_isoc(dep->endpoint.desc))
> > > + num_fifos = 2;
> > > +
> > > /* FIFO size for a single buffer */
> > > fifo = dwc3_gadget_calc_tx_fifo_size(dwc, 1);
> > > --
> > > 2.17.1
> > >
> > These settings are starting to get too specific for each application.
> > Can we find a better calculation?
> >
> > Perhaps something like this? (code not tested)
> >
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index 9a18973ebc05..d54b08f92aea 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -908,15 +908,10 @@ static int dwc3_gadget_resize_tx_fifos(struct dwc3_ep *dep)
> > ram1_depth = DWC3_RAM1_DEPTH(dwc->hwparams.hwparams7);
> > - if ((dep->endpoint.maxburst > 1 &&
> > - usb_endpoint_xfer_bulk(dep->endpoint.desc)) ||
> > + if (usb_endpoint_xfer_bulk(dep->endpoint.desc) ||
> > usb_endpoint_xfer_isoc(dep->endpoint.desc))
> > - num_fifos = 3;
> > -
> > - if (dep->endpoint.maxburst > 6 &&
> > - (usb_endpoint_xfer_bulk(dep->endpoint.desc) ||
> > - usb_endpoint_xfer_isoc(dep->endpoint.desc)) && DWC3_IP_IS(DWC31))
> > - num_fifos = dwc->tx_fifo_resize_max_num;
> > + num_fifos = min_t(unsigned int, dep->endpoint.maxburst + 1,
> > + dwc->tx_fifo_resize_max_num);
> > /* FIFO size for a single buffer */
> > fifo = dwc3_gadget_calc_tx_fifo_size(dwc, 1);
> >
> should be fine for me, as earlier there was no case handling for maxburst <=
> 1, by allocating fifo based on maxburst itself
>
> should be a good solution and will work for all as they customize based on
> maxburst through init scripts, let me test and update.
>

As I noted in the follow up response, you need to also account for
additional transaction opportunities for isoc if operating in highspeed.
(ie. use usb_endpoint_maxp_mult()).

BR,
Thinh