From: Joe Perches <joe@perches.com>
To: Michal Simek <michal.simek@xilinx.com>
Cc: netdev@vger.kernel.org,
"Peter Crosthwaite" <peter.crosthwaite@xilinx.com>,
"Sören Brinkmann" <soren.brinkmann@xilinx.com>,
monstr@monstr.eu, "John Linn" <John.Linn@xilinx.com>,
"Anirudha Sarangi" <anirudh@xilinx.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 02/12] net: axienet: Handle 0 packet receive gracefully
Date: Tue, 05 May 2015 11:53:49 -0700 [thread overview]
Message-ID: <1430852029.6575.13.camel@perches.com> (raw)
In-Reply-To: <554910D1.1030706@xilinx.com>
On Tue, 2015-05-05 at 20:49 +0200, Michal Simek wrote:
> On 05/05/2015 03:57 PM, Joe Perches wrote:
> > On Tue, 2015-05-05 at 11:25 +0200, Michal Simek wrote:
> >> From: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> >>
> >> 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.
> Is it really needed? If yes, no problem to add it but git blame can
> point you to that.
That's up to you.
I think that useful but concealed information is
always hard to follow or find.
next prev parent reply other threads:[~2015-05-05 18:53 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-05 9:25 [PATCH 01/12] net: axienet: Support for RGMII Michal Simek
2015-05-05 9:25 ` [PATCH 02/12] net: axienet: Handle 0 packet receive gracefully Michal Simek
2015-05-05 9:58 ` Shubhrajyoti Datta
2015-05-05 13:57 ` Joe Perches
2015-05-05 18:49 ` Michal Simek
2015-05-05 18:53 ` Joe Perches [this message]
2015-05-05 9:25 ` [PATCH 03/12] net: axienet: Service completion interrupts ASAP Michal Simek
2015-05-05 9:25 ` [PATCH 04/12] net: axienet: Handle jumbo frames for lesser frame sizes Michal Simek
2015-05-05 9:25 ` [PATCH 05/12] net: axienet: Support phy-less mode of operation Michal Simek
2015-05-05 9:25 ` [PATCH 06/12] net: axienet: Removed coding style errors and warnings Michal Simek
2015-05-05 9:26 ` [PATCH 07/12] net: axienet: Fix comments blocks Michal Simek
2015-05-05 9:26 ` [PATCH 08/12] net: axienet: Use pdev instead of op Michal Simek
2015-05-05 9:26 ` [PATCH 09/12] net: axienet: Use devm_* calls Michal Simek
2015-05-05 9:26 ` [PATCH 10/12] net: axienet: Use of_property_* calls Michal Simek
2015-05-05 9:26 ` [PATCH 11/12] net: axienet: Removed _of_ prefix in probe and remove functions Michal Simek
2015-05-05 9:26 ` [PATCH 12/12] net: axienet: Fix kernel-doc warnings Michal Simek
2015-05-05 12:54 ` [PATCH 01/12] net: axienet: Support for RGMII John Linn
2015-05-05 14:59 ` David Miller
2015-05-06 4:32 ` Florian Fainelli
2015-05-05 23:35 ` David Miller
2015-05-06 5:29 ` Michal Simek
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