drm/amdgpu: add a module parameter to control the AGP aperture

Add a module parameter to control the AGP aperture.  The AGP
aperture is an aperture in the GPU's internal address space
which provides direct non-paged access to the platform address
space.  This access is non-snooped so only uncached memory
can be accessed.

Add a knob so that we can toggle this for debugging.

Fixes: 67318cb8 ("drm/amdgpu/gmc11: set gart placement GC11")
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Tested-by: Mario Limonciello <mario.limonciello@amd.com> # PHX & Navi33
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -248,6 +248,7 @@ extern int amdgpu_umsch_mm;
 extern int amdgpu_seamless;
 
 extern int amdgpu_user_partt_mode;
+extern int amdgpu_agp;
 
 #define AMDGPU_VM_MAX_NUM_CTX			4096
 #define AMDGPU_SG_THRESHOLD			(256*1024*1024)

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -207,6 +207,7 @@ int amdgpu_user_partt_mode = AMDGPU_AUTO_COMPUTE_PARTITION_MODE;
 int amdgpu_umsch_mm;
 int amdgpu_seamless = -1; /* auto */
 uint amdgpu_debug_mask;
+int amdgpu_agp = -1; /* auto */
 
 static void amdgpu_drv_delayed_reset_work_handler(struct work_struct *work);
 
@@ -961,6 +962,15 @@ module_param_named(seamless, amdgpu_seamless, int, 0444);
 MODULE_PARM_DESC(debug_mask, "debug options for amdgpu, disabled by default");
 module_param_named(debug_mask, amdgpu_debug_mask, uint, 0444);
 
+/**
+ * DOC: agp (int)
+ * Enable the AGP aperture.  This provides an aperture in the GPU's internal
+ * address space for direct access to system memory.  Note that these accesses
+ * are non-snooped, so they are only used for access to uncached memory.
+ */
+MODULE_PARM_DESC(agp, "AGP (-1 = auto (default), 0 = disable, 1 = enable)");
+module_param_named(agp, amdgpu_agp, int, 0444);
+
 /* These devices are not supported by amdgpu.
  * They are supported by the mach64, r128, radeon drivers
  */

drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c

@@ -675,7 +675,7 @@ static void gmc_v10_0_vram_gtt_location(struct amdgpu_device *adev,
 	amdgpu_gmc_set_agp_default(adev, mc);
 	amdgpu_gmc_vram_location(adev, &adev->gmc, base);
 	amdgpu_gmc_gart_location(adev, mc, AMDGPU_GART_PLACEMENT_BEST_FIT);
-	if (!amdgpu_sriov_vf(adev))
+	if (!amdgpu_sriov_vf(adev) && (amdgpu_agp != 0))
 		amdgpu_gmc_agp_location(adev, mc);
 
 	/* base offset of vram pages */

drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c

@@ -641,7 +641,8 @@ static void gmc_v11_0_vram_gtt_location(struct amdgpu_device *adev,
 	amdgpu_gmc_vram_location(adev, &adev->gmc, base);
 	amdgpu_gmc_gart_location(adev, mc, AMDGPU_GART_PLACEMENT_HIGH);
 	if (!amdgpu_sriov_vf(adev) &&
-	    (amdgpu_ip_version(adev, GC_HWIP, 0) < IP_VERSION(11, 5, 0)))
+	    (amdgpu_ip_version(adev, GC_HWIP, 0) < IP_VERSION(11, 5, 0)) &&
+	    (amdgpu_agp != 0))
 		amdgpu_gmc_agp_location(adev, mc);
 
 	/* base offset of vram pages */

drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c

@@ -1630,7 +1630,7 @@ static void gmc_v9_0_vram_gtt_location(struct amdgpu_device *adev,
 	} else {
 		amdgpu_gmc_vram_location(adev, mc, base);
 		amdgpu_gmc_gart_location(adev, mc, AMDGPU_GART_PLACEMENT_BEST_FIT);
-		if (!amdgpu_sriov_vf(adev))
+		if (!amdgpu_sriov_vf(adev) && (amdgpu_agp != 0))
 			amdgpu_gmc_agp_location(adev, mc);
 	}
 	/* base offset of vram pages */