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

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Message-ID: <20240828234554.lw4hzeajneee7n55@synopsys.com>
Date: Wed, 28 Aug 2024 23:45:58 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: AKASH KUMAR <quic_akakum@...cinc.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jing Leng <jleng@...arella.com>, Felipe Balbi <balbi@...nel.org>,
        Jack Pham <quic_jackp@...cinc.com>,
        "kernel@...cinc.com" <kernel@...cinc.com>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Daniel Scally <dan.scally@...asonboard.com>,
        Vijayavardhan Vennapusa <quic_vvreddy@...cinc.com>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: gadget: Fix TX FIFO size for HS ISOC endpoints

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@...cinc.com>
> > > ---
> > >   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