[PATCH] tqma6: Fix DDR configuration

[Miquel Raynal]

Hi Fabio,

festevam at gmail.com wrote on Tue, 12 Dec 2023 13:11:53 -0300:

> On Fri, Nov 17, 2023 at 1:50 PM Miquel Raynal <miquel.raynal at bootlin.com> wrote:
> >
> > Initially investigating a Linux network issue causing a lot of drop and
> > poor network performances on a custom system based on a TQMA6A module
> > (based on an iMX6Q), [1st link below].
> >
> > I eventually correlated my observations with a contention at the NIC
> > level when in concurrency with the graphics pipeline. Troubleshooting
> > this in the kernel lead to disabling DMA bursts accesses made by the IPU
> > in order to avoid triggering the QoS at the interconnect level, reducing
> > from 50 to 10% the drop rate on eth0, [2nd link below]. The solution
> > worked on my setup but not on others, which still suffered from
> > abnormally high drop rates even with this "fix".
> >
> > After looking a while into TQ Systems BSP I figured out a number of
> > differences in recent U-Boot out-of-tree patches they had in their
> > repository [3rd link]. Parsing the differences one after the other lead
> > me to this final solution.
> >
> > The reset pad of the DDR controller was apparently misconfigured, Bit
> > 18-19 picturing the "DDR select field". The current value b11 is
> > reserved. The only defined value as of version 6 of the iMX6Q manual was
> > b00 "DDR3 and LPDDR2 mode". In practice no register difference has been
> > spotted after changing this configuration but all issues tracked thus
> > far just vanished. All previous fixes have been proven irrelevant. Just
> > clearing this field solved all our network issues and the drop rate as
> > measured by iperf3 felt back to 0%.
> >
> > Link: https://lore.kernel.org/netdev/20231012193410.3d1812cf@xps-13/
> > Link: https://lists.freedesktop.org/archives/dri-devel/2023-October/428251.html
> > Link: https://github.com/tq-systems/u-boot-tqmaxx/commit/15eb6abbefbf6916c28467b85485911dad3da6bc
> > Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>  
> 
> Applied, thanks.

Thanks a lot. Any chances you would have access to additional
information to explain how the network vs video pipeline
interact without this patch? I am eager to understand.

Cheers,
Miquèl