https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=281380
The LPDDR4 standard has optional support for on-die TRR.
This is the part number for the Micron 4GB SDRAM chip:
https://www.micron.com/support/tools-and-utilities/fbga?fbga=d9whv#pnlFBGA
Registration is required in order to get the datasheet for it.

As far as I'm aware, the SDRAM controller does not track row open/close counts so TRR isn't implemented.


Initialising SDRAM 'Samsung' 8Gb x1 total-size: 8 Gbit 3200       # 1gig model??
Initialising SDRAM 'Samsung' 16Gb x1 total-size: 16 Gbit 3200     # 2gig model??
Initialising SDRAM 'Micron' 16Gb x2 total-size: 32 Gbit 3200      # 4gig model
Initialising SDRAM 'Micron' 32Gb x2 total-size: 64 Gbit 3200      # 8gig model??