Change in coreboot[master]: nb/intel/x4x/raminit: Rework receive enable calibration

[Arthur Heymans (Code Review)]

Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/18692 )

Change subject: nb/intel/x4x/raminit: Rework receive enable calibration
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Patch Set 21:

(3 comments)

https://review.coreboot.org/#/c/18692/21/src/northbridge/intel/x4x/rcven.c
File src/northbridge/intel/x4x/rcven.c:

PS21, Line 40: #define SAMPLE_COUNT 3
does not seem to improve things.

PS21, Line 174: 	if (sampledqs(addr, lane, channel, DQS_HIGH)) {
              : 		printk(BIOS_WARNING, "DQS already HIGH... DQS probe is incosistent!\n"
              : 			"Continuing, but be cautious of possible instabilities.\n");
Is still being hit very consistently, so I think there is some hysteresis in this dram controller. I'll just documented it and maybe adapt printed message.

PS21, Line 218: 		/* Some settings are very noisy. Check the next tap */
              : 		/* if the result of the probe is consistent. */
              : 		if (sampledqs(addr, lane, channel, DQS_HIGH)) {
              : 			increase_tap(timing);
              : 			program_timing(timing, channel, lane);
              : 			if (sampledqs(addr, lane, channel, DQS_HIGH)) {
              : 				decrease_tap(timing);
              : 				program_timing(timing, channel, lane);
              : 				break;
              : 			} else {
              : 				decrease_tap(timing);
              : 			}
              : 		}
Does not seem to improve things since problems don't seem to be caused that much by noise but by hysteresis.