netdev - Re: RFC: [PATCH 1/3] usb: cdc

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Date:	Fri, 08 Mar 2013 16:28:59 -0600
From:	Dan Williams <dcbw@...hat.com>
To:	Loic Domaigne <loic.domaigne@...glemail.com>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: RFC: [PATCH 1/3] usb: cdc_ncm: patch for VMware

On Fri, 2013-03-08 at 22:03 +0100, Loic Domaigne wrote:
> This patch limits the Rx URB size to 16kB if the driver is compiled for a
> VMware environment. As of workstation 9, there are some major performance
> problems if the Rx URB size exceeds that limit.
> 
> This patch applies to longterm kernel version 3.4.35.
> 
> Signed-Off-By: Loic Domaigne <loic.domaigne@...bit.com> 
> 
> --- linux-3.4.35/drivers/net/usb/cdc_ncm.c.orig	2013-03-05 09:36:02.858740489 +0100
> +++ linux-3.4.35/drivers/net/usb/cdc_ncm.c	2013-03-05 10:20:18.092588668 +0100
> @@ -80,6 +80,23 @@
>  #define	CDC_NCM_TIMER_PENDING_CNT		2
>  #define CDC_NCM_TIMER_INTERVAL			(400UL * NSEC_PER_USEC)
>  
> +/* maximum Rx URB size */
> +/*
> + * in the original Linux driver, the rx urb size can be up to
> + * CDC_NCM_NTB_MAX_SIZE_RX.
> + *
> + * Under VMware (as of wks9), URB size greater than 16kB is a problem,
> + * so simply adjust this define when the driver is compiled for a VMware
> + * environment.
> + *
> + */
> +#ifdef VMWARE_BUG
> +#warning "Compiling for VMware"
> +#define CDC_NCM_MAX_RX_URB_SIZE     16384
> +#else
> +#define CDC_NCM_MAX_RX_URB_SIZE     CDC_NCM_NTB_MAX_SIZE_RX
> +#endif

I can't see how that is going to get past any sort of review.  Either
there's some other way of detecting that the CPU is the VMWare emulated
one or you're stuck with the bug until VMWare fixes it.

Dan

> +
>  /* The following macro defines the minimum header space */
>  #define	CDC_NCM_MIN_HDR_SIZE \
>  	(sizeof(struct usb_cdc_ncm_nth16) + sizeof(struct usb_cdc_ncm_ndp16) + \
> @@ -589,6 +606,9 @@ advance:
>  		ctx->out_ep->desc.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
>  	dev->status = ctx->status_ep;
>  	dev->rx_urb_size = ctx->rx_max;
> +	if (dev->rx_urb_size > CDC_NCM_MAX_RX_URB_SIZE)
> +		dev->rx_urb_size = CDC_NCM_MAX_RX_URB_SIZE;
> +	pr_debug("dev->rx_urb_size = %zu", dev->rx_urb_size);
>  
>  	/*
>  	 * We should get an event when network connection is "connected" or
> --
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