On Wed, Aug 19, 2026 at 12:33:56PM +0300, Jani Nikula wrote: > On Tue, 18 Aug 2026, Jani Nikula <[email protected]> wrote: > > On Sun, 16 Aug 2026, Chang Jiong(常炯) <[email protected]> wrote: > >> Since commit 2ee8dbd880b1 ("drm/i915/cdclk: Fix up CDCLK_FREQ_DECIMAL > >> without a full PLL re-enable") bxt_sanitize_cdclk() normalizes the > >> CD2X pipe select field of the CDCLK_CTL readback to PIPE_NONE before > >> comparing against the expected value. > >> > >> However bxt_cdclk_ctl() does not include the CD2X pipe select field > >> at all on DISPLAY_VER() >= 30, so on Xe3 (PTL) the normalized > >> readback (pipe field forced to the PIPE_NONE encoding, 0b111) can > >> never match the expected value (pipe field 0). The comparison now > >> fails on every boot and we always take the full CDCLK PLL > >> disable+re-enable path with the BIOS framebuffer actively scanning > >> out - exactly what this code was trying to avoid. On a Panther Lake > >> laptop (Arc B390, 8086:b080, eDP 3120x2080@120) this causes > >> "CPU pipe A FIFO underrun" during probe and persistent full-screen > >> scanout corruption for the first KMS client (the SDDM greeter); > >> the corruption lasts until the next full modeset. > >> > >> Only normalize the CD2X pipe select field on platforms where > >> bxt_cdclk_ctl() actually programs it, mirroring its DISPLAY_VER() > >> check. > >> > >> Fixes: 2ee8dbd880b1 ("drm/i915/cdclk: Fix up CDCLK_FREQ_DECIMAL without a > >> full PLL re-enable") > >> Cc: [email protected] > >> Signed-off-by: Chang Jiong(常炯) <[email protected]> > > > > Reviewed-by: Jani Nikula <[email protected]> > > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8550 > > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8569 > > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8901 > > > > The first one has a patch from Ville that is identical to this one. > > > > I'll try to kick CI to get this tested before merging. > > Okay, the patch is against some stable kernel, not against the current > development tree. Please rebase on top of the drm-tip branch of the > drm-tip repository.
I pushed my original fix and closed the other bugs as duplicates. -- Ville Syrjälä Intel
