Re: i.MX8/9: question about unused DDR PHY trained CSR board array

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Peng,

On 30.09.24 08:38, Peng Fan wrote:
>> Subject: i.MX8/9: question about unused DDR PHY trained CSR board
>> array
>> Looking at the DDR setup code for i.MX8M and i.MX9 that you had
>> contributed, I am wondering about struct
>> dram_cfg_param::ddrphy_trained_csr and the global
>> ddrphy_trained_csr array.
>>
>> struct dram_cfg_param::ddrphy_trained_csr is presumably generated
>> by the i.MX DDR tool and it seems populated by all the i.MX8M/9
>> boards in U-Boot.
>>
>> This struct member is wholly unused though and instead a global
>> ddrphy_trained_csr is used.
>>
>> What I wonder about is whether it's possible for the DDR tool to
>> generate a different ddrphy_trained_csr than the default:
>>
>>   1) If yes, we should drop the global ddrphy_trained_csr and actually
>> use
>>      the board-specific array
>>
>>   2) If not, we should drop the board-specific array and perhaps ask for
>>     the DDR tool to be changed
>>
>> I initially assumed 1) and because all boards supported by barebox had
>> a board-specific ddrphy_trained_csr that's identical to the global
>> ddrphy_trained_csr, I dropped the unused array[1][2].
>>
>> I now have the DDR settings for an i.MX9 LPDDR4 board in front of me
>> that has different contents for struct
>> dram_cfg_param::ddrphy_trained_csr than the default.
>>
>> I will inquire how that came about, but in parallel I wanted to ask you if
>> this is supposed to happen and to alert you to this issue.
> 
> Thanks for raising this issue. I think board specific csr should be used.
> 
> I will check with DDR TOOL owners on this.

Did you hear back in the meantime?

Thanks,
Ahmad

> 
>>
>> The way things are, this is either a bug or a missed space saving
>> opportunity for U-Boot.
> 
> Thanks,
> Peng.
> 
> 


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