Re: [PATCH v2 3/4] ddr: imx: Allow to call ddr init without logging failure

On 8/27/26 3:35 PM, Frieder Schrempf wrote:
> On 26.08.26 14:24, Marek Vasut wrote:
>> On 8/26/26 10:12 AM, Frieder Schrempf wrote:
>>
>> [...]
>>
>>>>> I'm not sure, but even if it would work, it would require several
>>>>> separate init attempts only to read the IDs
>>>>
>>>> Why ? Init the bus in slowest mode with widest bus settings, then try
>>>> MRRD on all available DRAM chips, then figure out which ones report
>>>> valid IDs and which ones fail the MRd .
>>>
>>> As far as I can see this doesn't work. If we use the widest bus setting
>>> (CsPresent=0x3) on a single rank module, the training fails and the DDR
>>> remains in a state where the MR read doesn't work yet.
>>
>> Do you need training to read the IDs ? Simply force-use the slowest bus
>> mode (100 MTps iirc), the training is only relevant for the high-speed
>> modes.
> I don't see any existing code path for any i.MX with DDR4 that doesn't
> do the training before accessing MR registers. Do you have any
> references or examples? Do you have any sources for the claim that the
> training is only relevant for the high-speed modes? I couldn't find
> anything that supports this.

What happens if you simply skip the DDR training, return 0 from 
ddr_cfg_phy() ?

> Also I would assume that doing the MRRD on an unused CS would give me
> back some arbitrary random values. While I could interpret an unknown
> value as "rank/cs not present", I don't think its reliable enough. Or do
> you know of any error condition being reported for failed MRRD?

Try it and see what happens ?