linux-kernel - Re: [PATCH v1 2/2] usb: gadget: dummy_hcd: Set transfer interval to 1 microframe

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Message-ID: <0b9e353b-2560-4884-b826-6ff26b933888@rowland.harvard.edu>
Date: Thu, 11 Apr 2024 12:21:46 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Marcello Sylvester Bauer <sylv@...v.io>
Cc: linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
  Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
  Marcello Sylvester Bauer <marcello.bauer@...ements.com>,
  Matthias Stoeckl <matthias.stoeckl@...unet.com>,
  Uwe Kleine-Koenig <u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH v1 2/2] usb: gadget: dummy_hcd: Set transfer interval to
 1 microframe

On Thu, Apr 11, 2024 at 05:22:11PM +0200, Marcello Sylvester Bauer wrote:
> Currently, the transfer polling interval is set to 1ms, which is the
> frame rate of full-speed and low-speed USB. The USB 2.0 specification
> introduces microframes (125 microseconds) to improve the timing
> precision of data transfers.
> 
> Reducing the transfer interval to 1 microframe increases data throughput
> for high-speed and super-speed USB communication
> 
> Signed-off-by: Marcello Sylvester Bauer <marcello.bauer@...ements.com>
> Signed-off-by: Marcello Sylvester Bauer <sylv@...v.io>
> ---
>  drivers/usb/gadget/udc/dummy_hcd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/dummy_hcd.c b/drivers/usb/gadget/udc/dummy_hcd.c
> index dab559d8ee8c..f37b0d8386c1 100644
> --- a/drivers/usb/gadget/udc/dummy_hcd.c
> +++ b/drivers/usb/gadget/udc/dummy_hcd.c
> @@ -50,6 +50,8 @@
>  #define POWER_BUDGET	500	/* in mA; use 8 for low-power port testing */
>  #define POWER_BUDGET_3	900	/* in mA */
>  
> +#define DUMMY_TIMER_INT_NSECS	125000 /* 1 microframe */

If the is_super_speed and is_high_speed module parameters are both false 
then the timer should run at 1-ms intervals.  So this needs to be 
something that can be adjusted at runtime, not a constant.

Alan Stern