From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Perches Subject: Re: [PATCH 02/12] net: axienet: Handle 0 packet receive gracefully Date: Tue, 05 May 2015 06:57:44 -0700 Message-ID: <1430834264.7191.9.camel@perches.com> References: <7fb84f65a61bbe0fdb4b61a871cf4d4f7910955d.1430817941.git.michal.simek@xilinx.com> <55b3c89b3549c61d62b8440636516fd572870842.1430817941.git.michal.simek@xilinx.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Peter Crosthwaite , =?ISO-8859-1?Q?S=F6ren?= Brinkmann , monstr@monstr.eu, John Linn , Anirudha Sarangi , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org To: Michal Simek Return-path: In-Reply-To: <55b3c89b3549c61d62b8440636516fd572870842.1430817941.git.michal.simek@xilinx.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, 2015-05-05 at 11:25 +0200, Michal Simek wrote: > From: Peter Crosthwaite > > The AXI-DMA rx-delay interrupt can sometimes be triggered > when there are 0 outstanding packets received. This is due > to the fact that the receive function will greedily consume > as many packets as possible on interrupt. So if two packets > (with a very particular timing) arrive in succession they > will each cause the rx-delay interrupt, but the first interrupt > will consume both packets. > This means the second interrupt is a 0 packet receive. > > This is mostly OK, except that the tail pointer register is > updated unconditionally on receive. Currently the tail pointer > is always set to the current bd-ring descriptor under > the assumption that the hardware has moved onto the next > descriptor. What this means for length 0 recv is the current > descriptor that the hardware is potentially yet to use will > be marked as the tail. This causes the hardware to think > its run out of descriptors deadlocking the whole rx path. > > Fixed by updating the tail pointer to the most recent > successfully consumed descriptor. I think some of this would be good to have as comments in the code instead of just in the changelog.