From 8edcda1266f93816fde77c9754f388ae0ae343fc Mon Sep 17 00:00:00 2001 From: Rodrigo Vivi Date: Fri, 15 Dec 2017 14:43:10 -0800 Subject: [PATCH] drm/i915: Protect DDI port to DPLL map from theoretical race. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit In case we have multiple modesets for different connectors happening in parallel we could have a race on the RMW on these shared registers. This possibility was initially raised by Paulo when reviewing commit '555e38d27317 ("drm/i915/cnl: DDI - PLL mapping")' but the original possibility comes from commit '5416d871136d ("drm/i915/skl: Set the eDP link rate on DPLL0")'. Or maybe later when atomic commits entered into picture. Apparently the discussion around this topic showed that the right solution would be on serializing the atomic commits in a way that we don't have the possibility of races here since if that parallel modeset happenings apparently many other things will be on fire. Code is there since SKL and there was no report of issue, but since we never looked back to that serialization possibility, and also we don't have an igt case for that it is better to at least protect this corner. Suggested-by: Paulo Zanoni Fixes: 555e38d27317 ("drm/i915/cnl: DDI - PLL mapping") Fixes: 5416d871136d ("drm/i915/skl: Set the eDP link rate on DPLL0") Cc: Paulo Zanoni Cc: Ville Syrjälä Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Signed-off-by: Rodrigo Vivi Reviewed-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20171215224310.19103-1-rodrigo.vivi@intel.com --- drivers/gpu/drm/i915/intel_ddi.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c index 369f780..f624ba8 100644 --- a/drivers/gpu/drm/i915/intel_ddi.c +++ b/drivers/gpu/drm/i915/intel_ddi.c @@ -2095,6 +2095,8 @@ static void intel_ddi_clk_select(struct intel_encoder *encoder, if (WARN_ON(!pll)) return; + mutex_lock(&dev_priv->dpll_lock); + if (IS_CANNONLAKE(dev_priv)) { /* Configure DPCLKA_CFGCR0 to map the DPLL to the DDI. */ val = I915_READ(DPCLKA_CFGCR0); @@ -2124,6 +2126,8 @@ static void intel_ddi_clk_select(struct intel_encoder *encoder, } else if (INTEL_INFO(dev_priv)->gen < 9) { I915_WRITE(PORT_CLK_SEL(port), hsw_pll_to_ddi_pll_sel(pll)); } + + mutex_unlock(&dev_priv->dpll_lock); } static void intel_ddi_clk_disable(struct intel_encoder *encoder) -- 2.7.4