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

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Message-ID: <20240827231552.7yokoe7jqdm3wduu@synopsys.com>
Date: Tue, 27 Aug 2024 23:15:56 +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 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);


Thanks,
Thinh