PC Graphics

[xiaolu]

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?

[lisa52smith]

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@xiaolu wrote:

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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The MST (Multi-Stream Transport) topology can indeed affect the FreeSync capability of your DFP (DisplayPort First-Priority) sink. When you connect your DP sink (Gigabyte FO32U2P) directly to the W7800 GPU via DP SST (Single-Stream Transport), the FreeSync capability is recognized correctly. However, when you introduce an MST hub into the setup, the FreeSync capability may be disabled due to how the MST hub handles the virtual DPCD (DisplayPort Configuration Data).

It seems that the MST hub completes the virtual DPCD, which might interfere with the FreeSync capability recognition. When you don't complete the virtual DPCD and directly reply with the SST sink peer type, the FreeSync capability is shown again. This suggests that the MST hub's handling of the DPCD is influencing the FreeSync capability.

To resolve this, you might need to check the MST hub's settings or firmware updates that could address this issue. Alternatively, you could try connecting the DP sink directly to the GPU without the MST hub if possible.

[xiaolu]

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?

[elstaci]

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/

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]

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]

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

[xiaolu]

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.