Re: [PATCH] drm/i915: Don't try to use negative pll_id.

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Nov 01, 2017 at 07:08:52PM +0000, Manasi Navare wrote:
> On Wed, Nov 01, 2017 at 11:44:58AM -0700, Rodrigo Vivi wrote:
> > It is unlikely we are getting the -1 here.
> > But if we propagate that pll_id -1 to the rest of the code
> > we might have funny calculations on link_clock and who
> > knows what registers we end up accessing.
> > 
> > Better to protect the code.
> > 
> > Also better with errno number instead of generic -1.
> > 
> > Cc: Manasi Navare <manasi.d.navare@intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_ddi.c      | 10 ++++++++++
> >  drivers/gpu/drm/i915/intel_dpll_mgr.c |  2 +-
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> > index ace674cd79b9..2c6abdbf33ea 100644
> > --- a/drivers/gpu/drm/i915/intel_ddi.c
> > +++ b/drivers/gpu/drm/i915/intel_ddi.c
> > @@ -1283,6 +1283,11 @@ static void cnl_ddi_clock_get(struct intel_encoder *encoder,
> >  
> >  	pll_id = intel_get_shared_dpll_id(dev_priv, pipe_config->shared_dpll);
> >  
> > +	if (pll_id < 0) {
> > +		DRM_ERROR("PLL not found\n");
> > +		return;
> > +	}
> > +
> 
> The function intel_get_shared_dpll_id() already has this WARN_ON:
> if (WARN_ON(pll < dev_priv->shared_dplls))
> and it return pll_id = (pll - dev_priv->shared_dplls);
> So shouldnt this already throw a warning in case pll < dev_priv->shared_dplls eventually
> resulting into a negative pll_id?

yeap, we through a warning and return -1.

Then we use the -1 to do some reg access and bits...

> 
> Manasi
> 
> >  	cfgcr0 = I915_READ(CNL_DPLL_CFGCR0(pll_id));
> >  
> >  	if (cfgcr0 & DPLL_CFGCR0_HDMI_MODE) {
> > @@ -1337,6 +1342,11 @@ static void skl_ddi_clock_get(struct intel_encoder *encoder,
> >  
> >  	pll_id = intel_get_shared_dpll_id(dev_priv, pipe_config->shared_dpll);
> >  
> > +	if (pll_id < 0) {
> > +		DRM_ERROR("PLL not found\n");
> > +		return;
> > +	}
> > +
> >  	dpll_ctl1 = I915_READ(DPLL_CTRL1);
> >  
> >  	if (dpll_ctl1 & DPLL_CTRL1_HDMI_MODE(pll_id)) {
> > diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> > index a83bf1c38e05..c4a7f39e173a 100644
> > --- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> > +++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> > @@ -102,7 +102,7 @@ intel_get_shared_dpll_id(struct drm_i915_private *dev_priv,
> >  {
> >  	if (WARN_ON(pll < dev_priv->shared_dplls||
> >  		    pll > &dev_priv->shared_dplls[dev_priv->num_shared_dpll]))
> > -		return -1;
> > +		return -ENOENT;
> >  
> >  	return (enum intel_dpll_id) (pll - dev_priv->shared_dplls);
> >  }
> > -- 
> > 2.13.6
> > 
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