Re: [PATCH 6/9] drm/i915/uncore: Don't meddle with mmio debug upon user forcewake

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 05 Nov 2026, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Currently when userspace takes the forcewake via debugfs, the
> kernel will stop looking for unclaimed mmio accesses. That link
> is kinda weird since forcewake is for GT stuff and unclaimed
> mmio detection is for display stuff.
>
> Just kill the mmio debug suspend/resume upon user forcewake.
> One should almost always use IGT_NO_FORCEWAKE=1 when poking
> at display register from userspace anyway so as to not
> perturb the rest of the system.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 46 ++---------------------------
>  drivers/gpu/drm/i915/intel_uncore.h |  2 --
>  2 files changed, 2 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index e360e4f9d9a2..abd695e880c1 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -65,41 +65,6 @@ intel_uncore_mmio_debug_init_early(struct drm_i915_private *i915)
>  	i915->uncore.debug = &i915->mmio_debug;
>  }
>  
> -static void mmio_debug_suspend(struct intel_uncore *uncore)
> -{
> -	if (!uncore->debug)
> -		return;
> -
> -	spin_lock(&uncore->debug->lock);
> -
> -	/* Save and disable mmio debugging for the user bypass */
> -	if (!uncore->debug->suspend_count++) {
> -		uncore->debug->saved_mmio_check = uncore->debug->unclaimed_mmio_check;
> -		uncore->debug->unclaimed_mmio_check = 0;
> -	}
> -
> -	spin_unlock(&uncore->debug->lock);
> -}
> -
> -static bool check_for_unclaimed_mmio(struct intel_uncore *uncore);
> -
> -static void mmio_debug_resume(struct intel_uncore *uncore)
> -{
> -	if (!uncore->debug)
> -		return;
> -
> -	spin_lock(&uncore->debug->lock);
> -
> -	if (!--uncore->debug->suspend_count)
> -		uncore->debug->unclaimed_mmio_check = uncore->debug->saved_mmio_check;
> -
> -	if (check_for_unclaimed_mmio(uncore))
> -		drm_info(&uncore->i915->drm,
> -			 "Invalid mmio detected during user access\n");
> -
> -	spin_unlock(&uncore->debug->lock);
> -}
> -
>  static const char * const forcewake_domain_names[] = {
>  	"render",
>  	"gt",
> @@ -598,9 +563,6 @@ check_for_unclaimed_mmio(struct intel_uncore *uncore)
>  
>  	lockdep_assert_held(&uncore->debug->lock);
>  
> -	if (uncore->debug->suspend_count)
> -		return false;
> -
>  	if (intel_uncore_has_fpga_dbg_unclaimed(uncore))
>  		ret |= fpga_check_for_unclaimed_mmio(uncore);
>  
> @@ -733,10 +695,8 @@ void intel_uncore_forcewake_get(struct intel_uncore *uncore,
>  void intel_uncore_forcewake_user_get(struct intel_uncore *uncore)
>  {
>  	spin_lock_irq(&uncore->lock);
> -	if (!uncore->user_forcewake_count++) {
> +	if (!uncore->user_forcewake_count++)
>  		intel_uncore_forcewake_get__locked(uncore, FORCEWAKE_ALL);
> -		mmio_debug_suspend(uncore);
> -	}
>  	spin_unlock_irq(&uncore->lock);
>  }
>  
> @@ -750,10 +710,8 @@ void intel_uncore_forcewake_user_get(struct intel_uncore *uncore)
>  void intel_uncore_forcewake_user_put(struct intel_uncore *uncore)
>  {
>  	spin_lock_irq(&uncore->lock);
> -	if (!--uncore->user_forcewake_count) {
> -		mmio_debug_resume(uncore);
> +	if (!--uncore->user_forcewake_count)
>  		intel_uncore_forcewake_put__locked(uncore, FORCEWAKE_ALL);
> -	}
>  	spin_unlock_irq(&uncore->lock);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
> index fafc2ca9a237..4ec7c545d04e 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.h
> +++ b/drivers/gpu/drm/i915/intel_uncore.h
> @@ -42,8 +42,6 @@ struct intel_gt;
>  struct intel_uncore_mmio_debug {
>  	spinlock_t lock; /** lock is also taken in irq contexts. */
>  	int unclaimed_mmio_check;
> -	int saved_mmio_check;
> -	u32 suspend_count;
>  };
>  
>  enum forcewake_domain_id {

-- 
Jani Nikula, Intel