[SRU][Q][PATCH 0/9] No output on external monitor when connecting to dell dock

[Aaron Ma]

There is a fix:
c65ee1b1ffc68 drm/i915/psr: Do not unnecessarily remove underrun on idle PSR WA
Fixes: 9b1795e9b0ae ("drm/i915/psr: Underrun on idle PSR wa only when
pkgc latency > delayed vblank")

Could you check if this fix should be applied too?

And there are 2 more patches are in this SRU:
4af5de27d3a9b drm/i915/display: Remove unused declarations of intel_io_*
9b1795e9b0ae6 drm/i915/psr: Underrun on idle PSR wa only when pkgc
latency > delayed vblank

I think the 2nd is metioned about underrun in section [Fix].
Could you add more explaination the 1st commit?

Thanks,
Aaron

On Fri, Dec 26, 2025 at 2:04 PM AceLan Kao <acelan.kao at canonical.com> wrote:
>
> From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>
>
> BugLink: https://bugs.launchpad.net/bugs/2131066
>
> [Impact]
> The 4k monitor on the dock is blank when connected to the device.
>
> [Fix]
> Intel provides a patch series to address this issue. The patches include
> fixes for Display Stream Compression (DSC) and Panel Self Refresh (PSR).
> One of the key changes refines a workaround for a PSR underrun issue,
> ensuring it is only applied under the correct conditions to prevent
> display problems on MST setups.
> https://patchwork.freedesktop.org/patch/686338/
>
> c390bf07961b drm/i915/dp: Fix panel replay when DSC is enabled
> 470b84af457e drm/i915/dp_mst: Recompute all MST link CRTCs if DSC gets enabled on the link
> 7c027070e98d drm/i915/dp_mst: Track DSC enabled status on the MST link
> b762ae48293e drm/i915/dp_mst: Reuse the DP-SST helper function to compute FEC config
> cb6c8f1f6f46 drm/i915/dp: Export helper to determine if FEC on non-UHBR links is required
> 69df31263bca drm/i915/dp: Ensure the FEC state stays disabled for UHBR links
> c88e70dc8bfc drm/i915/dsc: Add helper to enable the DSC configuration for a CRTC
>
> [Test]
> 1. Boot to OS, connect dell dock
> 2. Connect 4k monitor to dock, it should always work.
>
> [Where problems could occur]
> This series of patches touches advanced features in the Intel graphics
> driver, including Display Stream Compression (DSC), Panel Self Refresh (PSR),
> and Forward Error Correction (FEC), especially for DisplayPort Multi-Stream
> Transport (MST). Due to the complexity of these features, regressions
> could manifest in the following ways:
>
> - Flickering, link training failures (resulting in a blank screen), or other
>   visual corruption. These issues might occur with specific monitors or docks,
>   especially when using high resolutions or refresh rates.
>
> - The disabling of PSR for monitors on an MST link is a key part of the fix,
>   which will lead to increased power consumption in those configurations.
>
> - While aiming to fix a specific problem with a Dell dock, the changes could
>   inadvertently affect other hardware configurations that were previously
>   working correctly, leading to regressions on different docks or monitors.
>
>
> Gustavo Sousa (1):
>   drm/i915/display: Remove unused declarations of intel_io_*
>
> Imre Deak (7):
>   drm/i915/dsc: Add helper to enable the DSC configuration for a CRTC
>   drm/i915/dp: Ensure the FEC state stays disabled for UHBR links
>   drm/i915/dp: Export helper to determine if FEC on non-UHBR links is
>     required
>   drm/i915/dp_mst: Reuse the DP-SST helper function to compute FEC
>     config
>   drm/i915/dp_mst: Track DSC enabled status on the MST link
>   drm/i915/dp_mst: Recompute all MST link CRTCs if DSC gets enabled on
>     the link
>   drm/i915/dp: Fix panel replay when DSC is enabled
>
> Jouni Högander (1):
>   drm/i915/psr: Underrun on idle PSR wa only when pkgc latency > delayed
>     vblank
>
>  drivers/gpu/drm/i915/display/icl_dsi.c        |   2 +-
>  drivers/gpu/drm/i915/display/intel_display.c  |   2 +-
>  .../drm/i915/display/intel_display_types.h    |  15 ++-
>  drivers/gpu/drm/i915/display/intel_dp.c       |  34 ++++--
>  drivers/gpu/drm/i915/display/intel_dp.h       |   2 +
>  drivers/gpu/drm/i915/display/intel_dp_mst.c   |  31 ++---
>  drivers/gpu/drm/i915/display/intel_link_bw.c  |  17 +--
>  drivers/gpu/drm/i915/display/intel_link_bw.h  |   2 +-
>  drivers/gpu/drm/i915/display/intel_psr.c      | 109 ++++++++++++++++--
>  drivers/gpu/drm/i915/display/intel_vdsc.c     |  16 +++
>  drivers/gpu/drm/i915/display/intel_vdsc.h     |   2 +
>  drivers/gpu/drm/i915/display/skl_watermark.c  |   5 +
>  12 files changed, 187 insertions(+), 50 deletions(-)
>
> --
> 2.43.0
>
>
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