Re: [PATCH 1/2] drm/i915/cdclk: Avoid spurious cdclk sanitization on PTL+

On Fri, Jul 17, 2026 at 07:05:26PM +0300, Ville Syrjälä wrote:
> On Fri, Jul 17, 2026 at 06:51:06PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <[email protected]>
> > 
> > Apparently PTL+ no longer has the cd2x pipe select field in
> > CDCLK_CTL. Take that into account during CDCLK sanitization.
> > 
> > This currently triggers a spurious CDCLK sanitization during
> > driver load on PTL+ which will causes a visible glitch on all
> > active displays.
> > 
> > Cc: [email protected]
> > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8550
> > Fixes: 3f9de66f8acb ("drm/i915/cdclk: Fix up CDCLK_FREQ_DECIMAL without a full PLL re-enable")
> > Signed-off-by: Ville Syrjälä <[email protected]>
> > ---
> 
> Unfortunately the regression itself has a cc:stable on it, so we'll

it has a fixes tag, not a cc:stable itself, but yeah, that is enough to
reach the stable backports indeed...

> need to backport this fix as well.
> 
> To do that cleanly we need to pick up these as well:
> commit cd16e794aead ("drm/i915/cdclk: Clean up CDCLK_CTL defines")

you meant
commit aa8faabadc59 ("drm/i915/cdclk: Clean up CDCLK_CTL defines")
right?

> commit 67d77d9472c6 ("drm/i915/cdclk: Introduce bxt_cdclk_cd2x_pipe_mask() and use it")

I can pick these for the -fixes round, but for the stable we need to remember
to tell Greg and Sasha whenever we get their automated email saying that the
patch has failed to apply...

> 
> >  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 a53d88727177..9e5e15b0c4d1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > @@ -2381,8 +2381,10 @@ 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_mask(display);
> > -	cdctl |= bxt_cdclk_cd2x_pipe(display, INVALID_PIPE);
> > +	if (DISPLAY_VER(display) < 30) {
> > +		cdctl &= ~bxt_cdclk_cd2x_pipe_mask(display);
> > +		cdctl |= bxt_cdclk_cd2x_pipe(display, INVALID_PIPE);
> > +	}
> >  
> >  	if (cdctl != expected) {
> >  		if (DISPLAY_VER(display) < 20) {
> > -- 
> > 2.54.0
> 
> -- 
> Ville Syrjälä
> Intel