When I have my Dell UP2715k hooked up for 5k using its dual DP cable to two Thunderbolt 2 ports on a 2013 Mac Pro running 10.14.2, I can't get ddcctl to read or set brightness.
Dell's DDM monitor application works (looks like it also uses DDC/CI) with this dual DP setup in a Windows 10 Bootcamp install. And if I run the monitor in 4k on the Mac side with its single miniDP cable instead, ddcctl works great too.
Below is what I get running a debug install with the set and read brightness commands. I couldn't find any known issues with dual DP setups so I'm wondering if this limitation is already known or if there's any other output I can provide to help?
Great job BTW! Very cool to see this working when I used the single miniDP cable.
$ ddcctl -d 1 -b 50
2019-01-14 20:31:52.035 ddcctl[7327:988547] D: NSScreen #722475221 (2560x1440 0°) HiDPI
2019-01-14 20:31:52.035 ddcctl[7327:988547] I: found 1 external display
2019-01-14 20:31:52.036 ddcctl[7327:988547] I: polling display 1's EDID
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:14339 Serial:
2019-01-14 20:31:52.047 ddcctl[7327:988547] I: got edid.serial: F1JCM581085S
2019-01-14 20:31:52.048 ddcctl[7327:988547] I: got edid.name: DELL UP2715K
2019-01-14 20:31:52.048 ddcctl[7327:988547] D: action: b: 50
2019-01-14 20:31:52.048 ddcctl[7327:988547] D: setting VCP control #16 => 50
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:17695 Serial:
$ ddcctl -d 1 -b ?
2019-01-14 19:46:36.529 ddcctl[7108:899067] D: NSScreen #722475221 (2560x1440 0°) HiDPI
2019-01-14 19:46:36.529 ddcctl[7108:899067] I: found 1 external display
2019-01-14 19:46:36.529 ddcctl[7108:899067] I: polling display 1's EDID
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:17411 Serial:
2019-01-14 19:46:36.545 ddcctl[7108:899067] I: got edid.serial: F1JCM581085S
2019-01-14 19:46:36.545 ddcctl[7108:899067] I: got edid.name: DELL UP2715K
2019-01-14 19:46:36.545 ddcctl[7108:899067] D: action: b: ?
2019-01-14 19:46:36.545 ddcctl[7108:899067] D: querying VCP control: #16 =?
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:16683 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:14375 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:15911 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:14631 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:15655 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:15399 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:15143 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:14887 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:21799 Serial:
D: IOI2CTransactionTypes: 0x0f (15)
D: IOI2CNoTransactionType supported
D: IOI2CSimpleTransactionType supported
D: IOI2CDDCciReplyTransactionType supported
D: IOI2CCombinedTransactionType supported
E: IOI2CDisplayPortNativeTransactionType unsupported
Framebuffer: AMDFramebufferSI
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/GFXB@3/IOPP/GFX2@0/ATY,IkuraS@5/AMDFramebufferSI/display0/AppleDisplay
VN:37036 PN:16566 SN:808990035 UN:5 IN:22055 Serial:
E: No data after 10 tries!
2019-01-14 19:46:37.323 ddcctl[7108:899067] E: DDC send command failed!
2019-01-14 19:46:37.323 ddcctl[7108:899067] E: VCP control #16 (0x10) = current: 0, max: 0