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. Thanks, Jani. > >> --- >> v2: No code changes. Resent with From matching Signed-off-by >> (v1 was sent from [email protected], which is not on the >> Intel CI allowlist). >> >> drivers/gpu/drm/i915/display/intel_cdclk.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c >> b/drivers/gpu/drm/i915/display/intel_cdclk.c >> index 7bc9b956554b..0438f5ac78c0 100644 >> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c >> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c >> @@ -2366,8 +2366,10 @@ static void bxt_sanitize_cdclk(struct intel_display >> *display) >> * dividers both syncing to an active pipe, or asynchronously >> * (PIPE_NONE). >> */ >> - cdctl &= ~bxt_cdclk_cd2x_pipe(display, INVALID_PIPE); >> - cdctl |= bxt_cdclk_cd2x_pipe(display, INVALID_PIPE); >> + if (DISPLAY_VER(display) < 30) { >> + cdctl &= ~bxt_cdclk_cd2x_pipe(display, INVALID_PIPE); >> + cdctl |= bxt_cdclk_cd2x_pipe(display, INVALID_PIPE); >> + } >> >> if (cdctl != expected) { >> if (DISPLAY_VER(display) < 20) { -- Jani Nikula, Intel
