Subject: Re: Ethernet issue on imx6

From: Miquel Raynal <[email-masked]>
Date: Fri, 17 Nov 2023 16:09:28 +0100

Hello,

> I've investigated this further and found a strange relationship with
> the display subsystem. It seems like there is some congestion happening
> at the interconnect level. I wanted to point out that your hints helped
> as I observed that the above counters were incrementing as expected,
> but the packets were just not sent out. My interpretation is some
> kind of uDMA timeout caused by some hardware locking on the NIC by
> the IPU which cannot be diagnosed at the ENET level (the interrupt
> handler is firing but the skb's are not sent out, but we have no
> error status for that).
> 
> Here is the link of the thread I've just started with DRM people in
> order to really tackle this issue:
> https://lists.freedesktop.org/archives/dri-devel/2023-October/428251.html

For future reference, the thread mentioned above unfortunately did not
lead to any discussion (I admit it's not a common topic though) and
further investigation pointed at the DDR configuration. I had a hard
time making a link between the reset pad of the DDR controller being
misconfigured and the Ethernet drop rate, I still fail to do, but in
practice this very little change apparently had a significant impact and
totally solved our issue:
https://lore.kernel.org/u-boot/[email-masked]/

Thanks to all of you for your help and feedback,
Miquèl