Re: [PATCH] USB: change bInterval default to 10 ms

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Fri, 16 Sep 2016 10:24:26 -0400 (EDT)
Alan Stern <stern@rowland.harvard.edu> escreveu:

> Some full-speed mceusb infrared transceivers contain invalid endpoint
> descriptors for their interrupt endpoints, with bInterval set to 0.
> In the past they have worked out okay with the mceusb driver, because
> the driver sets the bInterval field in the descriptor to 1,
> overwriting whatever value may have been there before.  However, this
> approach was never sanctioned by the USB core, and in fact it does not
> work with xHCI controllers, because they use the bInterval value that
> was present when the configuration was installed.
> 
> Currently usbcore uses 32 ms as the default interval if the value in
> the endpoint descriptor is invalid.  It turns out that these IR
> transceivers don't work properly unless the interval is set to 10 ms
> or below.  To work around this mceusb problem, this patch changes the
> endpoint-descriptor parsing routine, making the default interval value
> be 10 ms rather than 32 ms.
> 
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> Tested-by: Wade Berrier <wberrier@gmail.com>
> CC: <stable@vger.kernel.org>

Acked-by: Mauro Carvalho Chehab <m.chehab@s-opensource.com>

> 
> ---
> 
> 
> [as1812]
> 
> 
>  drivers/usb/core/config.c |   28 +++++++++++++++++-----------
>  1 file changed, 17 insertions(+), 11 deletions(-)
> 
> Index: usb-4.x/drivers/usb/core/config.c
> ===================================================================
> --- usb-4.x.orig/drivers/usb/core/config.c
> +++ usb-4.x/drivers/usb/core/config.c
> @@ -240,8 +240,10 @@ static int usb_parse_endpoint(struct dev
>  	memcpy(&endpoint->desc, d, n);
>  	INIT_LIST_HEAD(&endpoint->urb_list);
>  
> -	/* Fix up bInterval values outside the legal range. Use 32 ms if no
> -	 * proper value can be guessed. */
> +	/*
> +	 * Fix up bInterval values outside the legal range.
> +	 * Use 10 or 8 ms if no proper value can be guessed.
> +	 */
>  	i = 0;		/* i = min, j = max, n = default */
>  	j = 255;
>  	if (usb_endpoint_xfer_int(d)) {
> @@ -250,13 +252,15 @@ static int usb_parse_endpoint(struct dev
>  		case USB_SPEED_SUPER_PLUS:
>  		case USB_SPEED_SUPER:
>  		case USB_SPEED_HIGH:
> -			/* Many device manufacturers are using full-speed
> +			/*
> +			 * Many device manufacturers are using full-speed
>  			 * bInterval values in high-speed interrupt endpoint
> -			 * descriptors. Try to fix those and fall back to a
> -			 * 32 ms default value otherwise. */
> +			 * descriptors. Try to fix those and fall back to an
> +			 * 8-ms default value otherwise.
> +			 */
>  			n = fls(d->bInterval*8);
>  			if (n == 0)
> -				n = 9;	/* 32 ms = 2^(9-1) uframes */
> +				n = 7;	/* 8 ms = 2^(7-1) uframes */
>  			j = 16;
>  
>  			/*
> @@ -271,10 +275,12 @@ static int usb_parse_endpoint(struct dev
>  			}
>  			break;
>  		default:		/* USB_SPEED_FULL or _LOW */
> -			/* For low-speed, 10 ms is the official minimum.
> +			/*
> +			 * For low-speed, 10 ms is the official minimum.
>  			 * But some "overclocked" devices might want faster
> -			 * polling so we'll allow it. */
> -			n = 32;
> +			 * polling so we'll allow it.
> +			 */
> +			n = 10;
>  			break;
>  		}
>  	} else if (usb_endpoint_xfer_isoc(d)) {
> @@ -282,10 +288,10 @@ static int usb_parse_endpoint(struct dev
>  		j = 16;
>  		switch (to_usb_device(ddev)->speed) {
>  		case USB_SPEED_HIGH:
> -			n = 9;		/* 32 ms = 2^(9-1) uframes */
> +			n = 7;		/* 8 ms = 2^(7-1) uframes */
>  			break;
>  		default:		/* USB_SPEED_FULL */
> -			n = 6;		/* 32 ms = 2^(6-1) frames */
> +			n = 4;		/* 8 ms = 2^(4-1) frames */
>  			break;
>  		}
>  	}
> 



Thanks,
Mauro