[U-Boot] [RFC] mpc83xx: add config options to spd_sdram

[Andre Schwarz]

York,
>>> I have made some mods to spd_sdram.c for various reason:
>>>
>>> 1.
>>> use SPD setup also for soldered RAM.
>>> This allows DDR mounting options without U-Boot change because SPD data
>>> is written during in-circuit/boundary-scan testing.
>> not sure I understand this - board with soldered RAM can't physically
>> get the SPD data from RAM, yet SPD data were somehow acquired and
>> written into some ROM, so spd_sdram() is still needed to parse&
>> program the controller without requiring a new u-boot binary?
>>
>> this isn't included in the below diff, right?
> Actually I have code for this already, pending for more broader testing.
> I use raw timing data from datasheet of DDR chips. We have an internal
> discussion to recommend using EEPROM to mimic SPD structure.
sorry - I don't understand this.
Why do you want to create something new if there's a standard
like SPD layout ? It is working perfectly fine and the data can be
obtained from the manufacturer without further modifications.

>>> 2.
>>> read SPD data also from extended adressing EEPROMS used for e.g. HRCW
>>> storage.
>>> Due to HRCW being being located at offset 0 we need an SPD data offset.
>> and this is the SPD_EEPROM_OFFSET stuff below?  hmm..
>>
>> so both 1&  2 are coagulated in my mind - ideally, this would be
>> implemented with the new ddr code in
>> arch/powerpc/cpu/mpc8xxx/ddr/main.c - see fsl_ddr_compute(), which has
>> a GET_SPD step that would need to be either skipped (i.e, start_step =
>> COMPUTE_DIMM_PARMS), or changed to be able to be overridden, or,
>> ideally, all DIMM computations would be precomputed and stored in ROM
>> and a direct start_step to e.g., STEP_ASSIGN_ADDRESSES were made.
> I don't 100% agree with the idea to put SPD-like data in HRCW.
The SPD data has nothing to do with HRCW - it's just stored in the same 
PROM.
>   How can you be sure the data matches DDR?
Because the SPD data gets programmed during production.
We can use any SPD table *exactly* matching the soldered parts.
> It would be equivalent to using fixed raw timing data, wouldn't it?
no - it isn't.
I want the *same* U-Boot binary running on *different* memory 
configurations, i.e.
*no* fixed timing at all.

>>> 3.
>>> for optimized signal integrity and power consumption we need more
>>> influence on
>>> the on-die termination. Although the assumed default values are working they
>>> are far from ideal.
>> board specific things like this are perfectly acceptable, of course.
>>
>> however, it should not be being done by glittering old-83xx/spd_sdram
>> with an extra #ifdef for every new parameter that is needed, especially
>> when this is all fixed in the new ddr code.  So, in preparation for
>> 83xx to eventually migrate to the new ddr code, I'd like this to be
>> done in such a way so as to start to conform to the new code by at least
>> defining ODT, etc. parameters in a board-specific
>> ddr.c:fsl_ddr_board_options().  See board/freescale/{p1022ds,*}/ddr.c
>> for example.
> The ODT table is implemented in options.c and it can be override by
> board functions. Look for the last function in options.c and  ddr.c
> under the board folder.

To me it is a fundamental design error to rely on environment data to set
up the hardware correctly. Especially something that critical as memory
configuration.

Do you expect U-Boot to work with a corrupted environment, i.e. hwconfig
value unavailable ?

Of course this might never happen on a reference design board - but 
that's not real life.

>>> 4.
>>> CPO values depend on internal bond wire length which has significantly
>>> high variance on MPC837x, i.e. this value also should be board specific.
>> again, to be defined as popts->cpo_override in the board-specific
>> ddr.c:fsl_ddr_board_options().
> I recommend to use auto calibration. If for some reason, you want to
> override, it belongs to board specific file, same as the above.
>
no - auto calibration is far from ideal regarding emc and power consumption.


Regards,
André

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