Re: drm/i915: Inline feature detection into sanitize_enable_ppgtt

From: Dan Carpenter <dan.carpenter@oracle.com>
To: chris@chris-wilson.co.uk
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: drm/i915: Inline feature detection into sanitize_enable_ppgtt
Date: Tue, 28 Oct 2014 13:52:51 +0300	[thread overview]
Message-ID: <20141028105251.GA7932@mwanda> (raw)

Hello Chris Wilson,

The patch 1893a71b1eba: "drm/i915: Inline feature detection into
sanitize_enable_ppgtt" from Sep 19, 2014, leads to the following
static checker warning:

	drivers/gpu/drm/i915/i915_gem_gtt.c:70 sanitize_enable_ppgtt()
	warn: we tested 'has_aliasing_ppgtt' before and it was 'true'

drivers/gpu/drm/i915/i915_gem_gtt.c
    36  static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
    37  {
    38          bool has_aliasing_ppgtt;
    39          bool has_full_ppgtt;
    40  
    41          has_aliasing_ppgtt = INTEL_INFO(dev)->gen >= 6;
    42          has_full_ppgtt = INTEL_INFO(dev)->gen >= 7;
    43          if (IS_GEN8(dev))
    44                  has_full_ppgtt = false; /* XXX why? */
    45  
    46          if (enable_ppgtt == 0 || !has_aliasing_ppgtt)
                                         ^^^^^^^^^^^^^^^^^^^
The patch introduces this condition.

    47                  return 0;
    48  
    49          if (enable_ppgtt == 1)
    50                  return 1;
    51  
    52          if (enable_ppgtt == 2 && has_full_ppgtt)
    53                  return 2;
    54  
    55  #ifdef CONFIG_INTEL_IOMMU
    56          /* Disable ppgtt on SNB if VT-d is on. */
    57          if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped) {
    58                  DRM_INFO("Disabling PPGTT because VT-d is on\n");
    59                  return 0;
    60          }
    61  #endif
    62  
    63          /* Early VLV doesn't have this */
    64          if (IS_VALLEYVIEW(dev) && !IS_CHERRYVIEW(dev) &&
    65              dev->pdev->revision < 0xb) {
    66                  DRM_DEBUG_DRIVER("disabling PPGTT on pre-B3 step VLV\n");
    67                  return 0;
    68          }
    69  
    70          return has_aliasing_ppgtt ? 1 : 0;
                       ^^^^^^^^^^^^^^^^^^
The patch introduces this already known condition.

    71  }

regards,
dan carpenter
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