From mboxrd@z Thu Jan  1 00:00:00 1970
From: 'Mika Westerberg' <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH net-next] net: thunderbolt: Clear finished Tx frame bus
 address in tbnet_tx_callback()
Date: Mon, 20 Nov 2017 17:05:16 +0200
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Cc: David Miller <davem@davemloft.net>,
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To: David Laight <David.Laight@ACULAB.COM>
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On Mon, Nov 20, 2017 at 02:46:53PM +0000, David Laight wrote:
> > There does not seem to be a way to mark DMA address invalid in a driver
> > so we probably need to add a flag to struct tbnet_frame instead.
> 
> Can you use the length?

Unfortunately no because size is 12-bit field in struct ring_frame and 0
means 4096 bytes.