[PATCH 1/2] drm/i915: Add a module option for disabling use of stolen memory

[Chris Wilson]

One of the first steps in triaging memory corruption on module load is
to disable stolen. (It helps reduce the impact of the BIOS clobbering
our memory since we allocate our ringbuffers and initial objects from
stolen, if they are clobbered we get an immediate hang and garbage on
screen.) Rather than requesting bug reporters patch their kernel to test
the theory, allow us to disable stolen through a module option.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_stolen.c | 5 +++++
 drivers/gpu/drm/i915/i915_params.c     | 6 ++++++
 drivers/gpu/drm/i915/i915_params.h     | 1 +
 3 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index 310756c30723..a47a1d63ecb6 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -411,6 +411,11 @@ int i915_gem_init_stolen(struct drm_device *dev)
 	}
 #endif
 
+	if (!i915.enable_stolen) {
+		DRM_INFO("Disabling use of stolen memory at user request.\n");
+		return 0;
+	}
+
 	if (ggtt->stolen_size == 0)
 		return 0;
 
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index b6e404c91eed..00986d98695c 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -61,6 +61,7 @@ struct i915_params i915 __read_mostly = {
 	.inject_load_failure = 0,
 	.enable_dpcd_backlight = false,
 	.enable_gvt = false,
+	.enable_stolen = true,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -120,6 +121,11 @@ MODULE_PARM_DESC(enable_hangcheck,
 	"WARNING: Disabling this can cause system wide hangs. "
 	"(default: true)");
 
+module_param_named(enable_stolen, i915.enable_stolen, bool, 0400);
+MODULE_PARM_DESC(enable_stolen,
+	"Enable use of memory reserved (stolen) by the BIOS for graphics. "
+	"(default: true)");
+
 module_param_named_unsafe(enable_ppgtt, i915.enable_ppgtt, int, 0400);
 MODULE_PARM_DESC(enable_ppgtt,
 	"Override PPGTT usage. "
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index 0ad020b4a925..a748577666eb 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -64,6 +64,7 @@ struct i915_params {
 	bool enable_dp_mst;
 	bool enable_dpcd_backlight;
 	bool enable_gvt;
+	bool enable_stolen;
 };
 
 extern struct i915_params i915 __read_mostly;
-- 
2.8.1