linux-kernel - Re: [PATCH 1/1] Drivers: hv: vmbus: Enable interrupt driven flow control

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Message-ID: <20140905191148.GA24879@kroah.com>
Date:	Fri, 5 Sep 2014 12:11:48 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	olaf@...fle.de, apw@...onical.com, jasowang@...hat.com
Subject: Re: [PATCH 1/1] Drivers: hv: vmbus: Enable interrupt driven flow
 control

On Fri, Sep 05, 2014 at 11:23:22AM -0700, K. Y. Srinivasan wrote:
> This is a win8 feature that has been implemented. Turn on the feature bit
> to enable the feature.

What does those two sentances even mean?

> With this feature turned on,

What is "this"?

> when the host is waiting
> for space to become available on the ringbuffer (host to guest), the guest
> will interrupt the host when space becomes available (as part of draining
> the ring buffer).
> 
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> ---
>  drivers/hv/ring_buffer.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 15db66b..6361d12 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -361,6 +361,11 @@ int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
>  	ring_info->ring_buffer->read_index =
>  		ring_info->ring_buffer->write_index = 0;
>  
> +	/*
> +	 * Set the feature bit for enabling flow control.
> +	 */
> +	ring_info->ring_buffer->feature_bits.value = 1;

What happens if you are running on an old system that doesn't support
this new "feature"?

thanks,

greg k-h
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