[Intel-gfx] [PATCH] drm/i915/display: Add missing checks for cdclk crawling

[Matt Roper]

On Thu, Nov 10, 2022 at 01:28:19PM +0200, Jani Nikula wrote:
> On Wed, 09 Nov 2022, Anusha Srivatsa <anusha.srivatsa at intel.com> wrote:
> > cdclk_sanitize() function was written assuming vco was a signed integer.
> > vco gets assigned to -1 (essentially ~0) for the case where PLL
> > might be enabled and vco is not a frequency that will ever
> > get used. In such a scenario the right thing to do is disable the
> > PLL and re-enable it again with a valid frequency.
> > However the vco is declared as a unsigned variable.
> > With the above assumption, driver takes crawl path when not needed.
> > Add explicit check to not crawl in the case of an invalid PLL.
> >
> > Cc: Matt Roper <matthew.d.roper at intel.com>
> > Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Signed-off-by: Anusha Srivatsa <anusha.srivatsa at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_cdclk.c | 2 ++
> >  drivers/gpu/drm/i915/display/intel_cdclk.h | 1 +
> >  2 files changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > index 8a9031012d74..91112d266763 100644
> > --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > @@ -1962,6 +1962,8 @@ static bool intel_cdclk_can_crawl(struct drm_i915_private *dev_priv,
> >  	if (!HAS_CDCLK_CRAWL(dev_priv))
> >  		return false;
> >  
> > +	if (intel_pll_is_unknown(a->vco))
> > +		return false;
> >  	/*
> >  	 * The vco and cd2x divider will change independently
> >  	 * from each, so we disallow cd2x change when crawling.
> > diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.h b/drivers/gpu/drm/i915/display/intel_cdclk.h
> > index c674879a84a5..6eb83d806f11 100644
> > --- a/drivers/gpu/drm/i915/display/intel_cdclk.h
> > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.h
> > @@ -80,6 +80,7 @@ intel_atomic_get_cdclk_state(struct intel_atomic_state *state);
> >  	to_intel_cdclk_state(intel_atomic_get_old_global_obj_state(state, &to_i915(state->base.dev)->display.cdclk.obj))
> >  #define intel_atomic_get_new_cdclk_state(state) \
> >  	to_intel_cdclk_state(intel_atomic_get_new_global_obj_state(state, &to_i915(state->base.dev)->display.cdclk.obj))
> > +#define intel_pll_is_unknown(vco)	((vco) == ~0)
> 
> Why here? What does a pll function do in intel_cdclk.h?

Since this is referring to the cdclk pll (not port pll's), I suspect
this shouldn't be needed anywhere outside the cdclk code.  So it might
be best just make this a static function inside the cdclk .c file rather
than placing it in a header that exposes it to the rest of the driver.
I.e., something like:

        static bool pll_us_unknown(struct intel_cdclk_state *s) {
                return (s->vco == ~0);
        }


Matt

> 
> BR,
> Jani.
> 
> >  
> >  int intel_cdclk_init(struct drm_i915_private *dev_priv);
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation