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

[Manasi Navare]

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 at intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at 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?

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
>