lkml.org 
[lkml]   [2015]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 02/12] net: axienet: Handle 0 packet receive gracefully
From
Date
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.




\
 
 \ /
  Last update: 2015-05-05 21:21    [W:0.063 / U:1.176 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site