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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Jul 17, 2026 at 06:51:06PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> 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: stable@vger.kernel.org
> 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 <ville.syrjala@linux.intel.com>
> ---

Unfortunately the regression itself has a cc:stable on it, so we'll
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")
commit 67d77d9472c6 ("drm/i915/cdclk: Introduce bxt_cdclk_cd2x_pipe_mask() and use it")

>  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