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

Hello Peng,

On 30.09.24 08:38, Peng Fan wrote:

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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

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

Thanks, Peng.