I have an issue related to the busfreq driver on our custom i.mx7 design. Up until our latest (2nd) build we've had no issues, however with our latest build, roughly 30% of the boards are locking up when busfreq drops the clock down to 24MHz.
One key different between the builds is that the 16bit DDR3 part has changed from a Micron part to an alliance part:
Previous part: MT41K256M16TW-107
New part: AS4C256M16D3LB-12BIN
I couldn't be missing something, but from what I can read in the datasheets, there is no reason for the new alliance part to not work. And it does for most of the 15 boards built so far.
I have run the DDR v2.70 stress tool on various boards at various frequencies (350-533). All pass regardless of the DDR and the calibration result values are all the very close to the same. The stress test tool does not allow to run tests the the lower power mode (24MHz), at least not the u-boot variant, so I am not able to test at that frequency using this tool.
I've also slightly modofied the busreq driver to go to the "audio mode" (100MHz) instead of the low power mode (24MHz). I get the same results with this change (i.e. some boards work ok and some boards lock up as soon as the clock is changing).
I did see this post which may or may not be related, however i didn't draw any conclusions from it:
Any advice is appreciated.