So, as I was iotracing atombios execution from within linux. The hardware connection is pretty straightforward: AMD Trinity DP0 -> RTD2132 -> LVDS panel. I noticed a set of very interesting DPCD accesses [1], to registers marked as "RESERVED for Branch device usage" by the Display Port spec.
Looking carefully at how those accesses are done, it seems 0x5f0/0x5f1 are a big-endian index port, and 0x5f3 is the data port. Most likely, these lead to some internal register space of the RTD2132. Whether this is the same as the I2C space or not is unknown at this time.
So, for those of you who had worked with this chip before, do these accesses look familiar? I wasn't able to find any sources that mess with the RTD2132 on the DPCD level.
Alex
=== Appendix [1]: RAW DPCD channel transactions ===
0x5f0 <- 0x00, 0x02 0x5f2 -> 0x20 0x5f0 <- 0x00, 0x03 0x5f2 -> 0x31 0x5f0 <- 0x00, 0x05, 0x3d 0x5f0 <- 0x00, 0x1f, 0x03 0x5f0 <- 0x00, 0xba, 0x00 0x5f0 <- 0x00, 0xbb, 0x08 0x5f0 <- 0x00, 0xb1, 0x4b 0x5f0 <- 0x01, 0x73, 0x69 0x5f0 <- 0x01, 0x9f, 0x24 0x5f0 <- 0x00, 0x19, 0x33 0x5f0 <- 0x00, 0x89, 0x39 0x5f0 <- 0x00, 0xf8, 0x42 0x5f0 <- 0x00, 0xf9, 0x01 0x5f0 <- 0x00, 0xfa, 0x23 0x5f0 <- 0x00, 0xfb, 0x45 0x5f0 <- 0x00, 0xfc, 0x67 0x5f0 <- 0x00, 0xfd, 0x89 0x5f0 <- 0x00, 0xfe, 0xab 0x5f0 <- 0x00, 0x1d, 0x25 0x5f0 <- 0x01, 0xc3, 0x07 0x5f0 <- 0x01, 0xc2, 0x5a 0x5f0 <- 0x01, 0xc4, 0x03 0x5f0 <- 0x01, 0xc0, 0x07 0x5f0 <- 0x01, 0xc1, 0x5a 0x5f0 <- 0x01, 0xb1, 0x03 0x5f0 <- 0x01, 0xbf, 0x7d 0x5f0 <- 0x01, 0xb5, 0x63 0x5f0 <- 0x01, 0xcb, 0x80 0x5f0 <- 0x01, 0xb3, 0x66 0x5f0 <- 0x01, 0xb2, 0x9a 0x5f0 <- 0x00, 0x9f, 0x00 0x5f0 <- 0x01, 0x83, 0x14 0x5f0 <- 0x00, 0xa7, 0xc2 0x5f0 <- 0x01, 0x71, 0x12 0x5f0 <- 0x01, 0x82, 0x5d 0x5f0 <- 0x01, 0x89, 0x28 0x5f0 <- 0x01, 0xbe, 0x01 0x5f0 <- 0x00, 0x8a, 0x53 0x5f0 <- 0x00, 0x0a, 0x01 0x5f0 <- 0x01, 0xd4, 0x10 0x5f0 <- 0x00, 0xf3, 0x00 0x5f0 <- 0x00, 0xf4, 0x3c 0x5f0 <- 0x01, 0xb4, 0x06 0x5f0 <- 0x00, 0xdc, 0x00 0x5f0 <- 0x00, 0xdd, 0x00 0x5f0 <- 0x01, 0x91, 0x20 0x5f0 <- 0x00, 0xd1, 0x06 0x5f0 <- 0x00, 0xd6, 0x01 0x5f0 <- 0x01, 0xd2, 0x08 0x5f0 <- 0x01, 0xd3, 0x80
=== Appendix [2]: Presumed accesses to RTD2132 internal register space ===
READ: 0x0002 -> 0x02 READ: 0x0003 -> 0x31 WRITE: 0x0005 <- 3d WRITE: 0x001f <- 03 WRITE: 0x00ba <- 00 WRITE: 0x00bb <- 08 WRITE: 0x00b1 <- 4b WRITE: 0x0173 <- 69 WRITE: 0x019f <- 24 WRITE: 0x0019 <- 33 WRITE: 0x0089 <- 39 WRITE: 0x00f8 <- 42 WRITE: 0x00f9 <- 01 WRITE: 0x00fa <- 23 WRITE: 0x00fb <- 45 WRITE: 0x00fc <- 67 WRITE: 0x00fd <- 89 WRITE: 0x00fe <- ab WRITE: 0x001d <- 25 WRITE: 0x01c3 <- 07 WRITE: 0x01c2 <- 5a WRITE: 0x01c4 <- 03 WRITE: 0x01c0 <- 07 WRITE: 0x01c1 <- 5a WRITE: 0x01b1 <- 03 WRITE: 0x01bf <- 7d WRITE: 0x01b5 <- 63 WRITE: 0x01cb <- 80 WRITE: 0x01b3 <- 66 WRITE: 0x01b2 <- 9a WRITE: 0x009f <- 00 WRITE: 0x0183 <- 14 WRITE: 0x00a7 <- c2 WRITE: 0x0171 <- 12 WRITE: 0x0182 <- 5d WRITE: 0x0189 <- 28 WRITE: 0x01be <- 01 WRITE: 0x008a <- 53 WRITE: 0x000a <- 01 WRITE: 0x01d4 <- 10 WRITE: 0x00f3 <- 00 WRITE: 0x00f4 <- 3c WRITE: 0x01b4 <- 06 WRITE: 0x00dc <- 00 WRITE: 0x00dd <- 00 WRITE: 0x0191 <- 20 WRITE: 0x00d1 <- 06 WRITE: 0x00d6 <- 01 WRITE: 0x01d2 <- 08 WRITE: 0x01d3 <- 80