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A device may reference one DART stream per controller it uses. The Apple display-subsystem lists one scanout DART (stream 0) per DCP; on M2 Max, wiring all four external DCPs (dcpext0..3) plus disp0 needs five. The cap of 3 makes apple_dart_of_xlate() reject the extra streams with -EINVAL, so the later DCPs never get a scanout mapping and their firmware faults on the first frame. Raise the cap to 8.
The M2 Max die has four external display controllers, but only dcpext0 (HDMI + Type-C) and dcpext1 (Type-C) were described. Add dcpext2 and dcpext3 as further Type-C route candidates in a new t6021-display2.dtsi, included by the M2 Max laptop boards (j414c/j416c) only -- M2 Pro (t6020) has two external DCPs. This lets the machine drive its internal panel plus HDMI and three Type-C displays at once. Needs MAX_DARTS_PER_DEVICE >= 5 (previous patch): the display-subsystem now lists five scanout DARTs.
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Wire the M2 Max's two unused external display controllers so the machine can
drive its internal panel plus HDMI and three Type-C displays at once
(previously internal + two externals).
iommu: apple-dart: raise MAX_DARTS_PER_DEVICE to 8
The display-subsystem lists one scanout DART (stream 0) per DCP. Wiring all
four M2 Max external DCPs (dcpext0..3) plus disp0 needs five; the cap of 3
made
apple_dart_of_xlate()reject the extras with-EINVAL, so the laterDCPs got no scanout mapping and their firmware faulted on the first frame
(
axi_rd_err).arm64: dts: apple: t6021: add dcpext2/dcpext3 external displays
New
t6021-display2.dtsi(dcpext2/dcpext3: own DART/dispext-DART/mailbox/fixed-clock, crossbar states 4/6, typec-routes to all three ports, aliases so
m1n1 reserves their firmware, and the dispext2/3 DARTs added to the
display-subsystem), included by the M2 Max laptop boards (j414c/j416c) only.
M2 Pro (t6020) has two external DCPs and is untouched.
Tested on an M2 Max (j416c) at this pin (38c14f6): internal 3456x2160@120 +
HDMI (LG 4096x2160@60) + three Type-C (C49RG9x 5120x1440@120, C34H89x
3440x1440, +3440x1440) = five displays; all five DCPs booted
(389c/289c/315c/48dc/50dc); zero DCP crashes,
axi_rd_err0.