Re: [PATCH] tqma6: Fix DDR configuration

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Alexander,

> > > > --- a/board/tq/tqma6/tqma6q.cfg
> > > > +++ b/board/tq/tqma6/tqma6q.cfg
> > > > @@ -36,7 +36,7 @@ DATA 4, MX6_IOM_DRAM_SDCLK_1, 0x00008030
> > > > 
> > > >  DATA 4, MX6_IOM_DRAM_CAS, 0x00008030
> > > >  DATA 4, MX6_IOM_DRAM_RAS, 0x00008030
> > > >  DATA 4, MX6_IOM_GRP_ADDDS, 0x00000030
> > > > 
> > > > -DATA 4, MX6_IOM_DRAM_RESET, 0x000C3030
> > > > +DATA 4, MX6_IOM_DRAM_RESET, 0x00003030  
> > > 
> > > Thank you for pointing this out. Originally this error came from an
> > > older/ancient reference manual. Sorry that we missed to bring this
> > > upstream. We will send the changes for DCD data in the next days.  
> > 
> > No problem, I'm glad this can now be solved. By any chance, could you
> > point to the relevant location of the manual (ddr or imx6 ?) explaining
> > what this is actually about? Because I failed to bring any real
> > explanation to my observations so far.  
> 
> It's a bit hidden but the comment above that list indicates these settings are 
> iomuxc configurations. In this case the register 
> IOMUXC_SW_PAD_CTL_PAD_DRAM_RESET. See i.MX6Q RM Rev.6 05/2020 section 
> 36.4.347.
> Your patch configures the field "DDR Select Field" from reserved3 to 
> DDR3_LPDDR2. It seems this field has to be set to 0 in every case.

Yes, that's also what I get from reading the iMX6Q manual. But I'm
sorry I don't understand why a runtime change of a reset pin
configuration can be so impacting. It's not like it only affects the
power-on sequence because I can reproduce the strange QoS/NIC issues
with a devmem once the kernel has started. I  believe there is a bit
more than just a pad configuration behind this field.

Thanks,
Miquèl