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PC Graphics

xiaolu
Adept I
3 weeks ago

can not see the Freesync capibility when MST HUB connect to DP out

I use the AMD W7800 GPU.

I have a DP sink Gigabyte FO32U2P with Freesync capibility, and I can see the Freesync capibility in AMD GPU tool when this sink directly connect to W7800 by DP SST.

Then I connect this sink to MST HUB DFP, and connect this MST HUB to W7800 DP out, the Freesync capibility become disabled status.

I capture the MST HUB UFP DP aux log, and ensure that this MST HUB complete the virtual DPCD, and it support MSA_ignored capibility, if I try to do not

complete the virtual DPCD(directly reply the sst sink peer type in lct=1 link_address reply), the Freesync capibility can show.

So May I know what influence that the MST topology have on the DFP sink Freesync capibility?

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7 Replies
xiaolu
In response to lisa52smith
Adept I
3 weeks ago

Thanks. I must need use the MST HUB in my usage case, so I want to know how to fix this issue

in the case of MST HUB with virtual DPCD implement.

Maybe some virtual DPCD read by AMD remote DPCD read down request have influence on this phenomenon? I only know the MSA_ignored bit in DPCD0007 bit0 is related to Freesync and I ensure this bit is set in MST HUB virtual DPCD, and I analyze the aux log, not other related DPCD that AMD read. Maybe AMD driver disable the Freesync when MST topology have two and more layer?

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elstaci
In response to xiaolu
MVP
3 weeks ago

See if your MST support Freesync or not.

 

Found this MST That support G-sync and Freesync: https://www.club-3d.com/en/quick-view/2486/

Screenshot 2025-01-05 125119.png

 

EDIT: Just realize you have a Professional GPU card. Possibly AMD Moderator of Pro GPUs can assist you with your issue @fsadough 

 

But personally it might sound like your MST might not fully nor be compatible with Freesync if you said that Freesync is enabled for your Pro GPU card.

xiaolu
In response to elstaci
Adept I
2 weeks ago

Thanks. I think my MST HUB is compatiable to Freesync because I review its UFP and virtual DPCD data of MSA_ignored bit, and the Freesync is enabled when virtual DPCD do not implement in this MST HUB.

So what I wonder is that the influence of virtual DPCD implement on the freesync.

atmosphere
In response to xiaolu
Challenger
2 weeks ago

It probably lets the hub go around issue with DRM/HDCP when cloning outputs... MST could be reprojecting input, taking output params of top prio output or defaulting to a hardware default (native @60Hz, common 8b colorchannels to be sure that all plugged in can be fed from one feed.. and not all screens support adaptive sync even.. which would lead to weird issues, or expensive & active mst hardware..  

 

Also (mon)--DP-->(mst)--DP-->(w7800)? Just to be sure

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atmosphere
Challenger
3 weeks ago

Does the hub offer the same scanrange as the monitor? Is it chained with other devices?

xiaolu
In response to atmosphere
Adept I
2 weeks ago

No other sink connect to this MST HUB. My topology is w7800->MST HUB->Gigabyte FO32U2P.

The hub offer the same scanrange as this sink, display timing is right.

atmosphere
In response to xiaolu
Challenger
2 weeks ago

Not all mst-hubs support freesync or adaptive sync. What mst hub are you using, if you can be specific about that?

 

How many outputs are there on the mst? Does connecting to one of the other change anything?

And with the MST you use 2 cables ... if you connect either directly to test only.. do both give you freesync capability