drm/i915/gvt: introduce intel_vgpu_reset_cfg_space to reset configuration space

This patch introduces a new function intel_vgpu_reset_cfg_space()
to reset vGPU configuration space. This function will unmap gttmmio
and aperture if they are mapped before. Then entire cfg space will
be restored to default values.

Currently we only do such reset when vGPU is not owned by any VM
so we simply restore entire cfg space to default value, not following
the PCIe FLR spec that some fields should remain unchanged.
Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/cfg_space.c

@@ -331,3 +331,28 @@ void intel_vgpu_init_cfg_space(struct intel_vgpu *vgpu,
 		vgpu->cfg_space.bar[i].tracked = false;
 	}
 }
+
+/**
+ * intel_vgpu_reset_cfg_space - reset vGPU configuration space
+ *
+ * @vgpu: a vGPU
+ *
+ */
+void intel_vgpu_reset_cfg_space(struct intel_vgpu *vgpu)
+{
+	u8 cmd = vgpu_cfg_space(vgpu)[PCI_COMMAND];
+	bool primary = vgpu_cfg_space(vgpu)[PCI_CLASS_DEVICE] !=
+				INTEL_GVT_PCI_CLASS_VGA_OTHER;
+
+	if (cmd & PCI_COMMAND_MEMORY) {
+		trap_gttmmio(vgpu, false);
+		map_aperture(vgpu, false);
+	}
+
+	/**
+	 * Currently we only do such reset when vGPU is not
+	 * owned by any VM, so we simply restore entire cfg
+	 * space to default value.
+	 */
+	intel_vgpu_init_cfg_space(vgpu, primary);
+}

drivers/gpu/drm/i915/gvt/gvt.h

@@ -414,6 +414,8 @@ int intel_gvt_ggtt_h2g_index(struct intel_vgpu *vgpu, unsigned long h_index,
 
 void intel_vgpu_init_cfg_space(struct intel_vgpu *vgpu,
 		bool primary);
+void intel_vgpu_reset_cfg_space(struct intel_vgpu *vgpu);
+
 int intel_vgpu_emulate_cfg_read(struct intel_vgpu *vgpu, unsigned int offset,
 		void *p_data, unsigned int bytes);