nvidia: add NVreg_ForceExternalGpu module parameter

Thunderbolt 4/5 eGPU enclosures fail automatic external GPU detection
because they are not in the approved TB3 bridge list and do not report
the required slot capabilities (HotPlug+ and Surprise+).

Add NVreg_ForceExternalGpu parameter to bypass bridge detection and
unconditionally set PDB_PROP_GPU_IS_EXTERNAL_GPU, enabling proper eGPU
handling throughout the driver.

Author: roger-pmta

kernel-open/nvidia/nv-reg.h

@@ -672,6 +672,28 @@
 #define NV_REG_TEGRA_GPU_PG_MASK \
     NV_REG_STRING(__NV_TEGRA_GPU_PG_MASK)
 
+/*
+ * Option: ForceExternalGpu
+ *
+ * Description:
+ *
+ * When this option is enabled, the NVIDIA driver will treat all GPUs as
+ * external GPUs (eGPU), bypassing the automatic Thunderbolt bridge detection.
+ * This is useful for Thunderbolt 4/5 enclosures that are not in the driver's
+ * approved bridge whitelist.
+ *
+ * When enabled, the Platform Request Handler (power management) is disabled
+ * for these GPUs, which can prevent link training issues on eGPU setups.
+ *
+ * Possible values:
+ *
+ *  0 - use automatic eGPU detection (default)
+ *  1 - force all GPUs to be treated as external GPUs
+ */
+
+#define __NV_FORCE_EXTERNAL_GPU ForceExternalGpu
+#define NV_REG_FORCE_EXTERNAL_GPU NV_REG_STRING(__NV_FORCE_EXTERNAL_GPU)
+
 /*
  * Option: RegisterPCIDriver
  *
@@ -1000,6 +1022,7 @@ NV_DEFINE_REG_ENTRY(__NV_DYNAMIC_POWER_MANAGEMENT_VIDEO_MEMORY_THRESHOLD, 200);
 NV_DEFINE_REG_ENTRY(__NV_ENABLE_GPU_FIRMWARE, NV_REG_ENABLE_GPU_FIRMWARE_DEFAULT_VALUE);
 NV_DEFINE_REG_ENTRY(__NV_ENABLE_GPU_FIRMWARE_LOGS, NV_REG_ENABLE_GPU_FIRMWARE_LOGS_ENABLE_ON_DEBUG);
 NV_DEFINE_REG_ENTRY(__NV_OPENRM_ENABLE_UNSUPPORTED_GPUS, 1);
+NV_DEFINE_REG_ENTRY(__NV_FORCE_EXTERNAL_GPU, 0);
 
 NV_DEFINE_REG_ENTRY_GLOBAL(__NV_ENABLE_USER_NUMA_MANAGEMENT, 1);
 NV_DEFINE_REG_ENTRY_GLOBAL(__NV_MEMORY_POOL_SIZE, 0);
@@ -1076,6 +1099,7 @@ nv_parm_t nv_parms[] = {
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_RM_NVLINK_BW_LINK_COUNT),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_ENABLE_DBG_BREAKPOINT),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_OPENRM_ENABLE_UNSUPPORTED_GPUS),
+    NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_FORCE_EXTERNAL_GPU),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_DMA_REMAP_PEER_MMIO),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_IMEX_CHANNEL_COUNT),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_CREATE_IMEX_CHANNEL_0),

src/nvidia/arch/nvalloc/unix/include/nv-reg.h

@@ -672,6 +672,28 @@
 #define NV_REG_TEGRA_GPU_PG_MASK \
     NV_REG_STRING(__NV_TEGRA_GPU_PG_MASK)
 
+/*
+ * Option: ForceExternalGpu
+ *
+ * Description:
+ *
+ * When this option is enabled, the NVIDIA driver will treat all GPUs as
+ * external GPUs (eGPU), bypassing the automatic Thunderbolt bridge detection.
+ * This is useful for Thunderbolt 4/5 enclosures that are not in the driver's
+ * approved bridge whitelist.
+ *
+ * When enabled, the Platform Request Handler (power management) is disabled
+ * for these GPUs, which can prevent link training issues on eGPU setups.
+ *
+ * Possible values:
+ *
+ *  0 - use automatic eGPU detection (default)
+ *  1 - force all GPUs to be treated as external GPUs
+ */
+
+#define __NV_FORCE_EXTERNAL_GPU ForceExternalGpu
+#define NV_REG_FORCE_EXTERNAL_GPU NV_REG_STRING(__NV_FORCE_EXTERNAL_GPU)
+
 /*
  * Option: RegisterPCIDriver
  *
@@ -1000,6 +1022,7 @@ NV_DEFINE_REG_ENTRY(__NV_DYNAMIC_POWER_MANAGEMENT_VIDEO_MEMORY_THRESHOLD, 200);
 NV_DEFINE_REG_ENTRY(__NV_ENABLE_GPU_FIRMWARE, NV_REG_ENABLE_GPU_FIRMWARE_DEFAULT_VALUE);
 NV_DEFINE_REG_ENTRY(__NV_ENABLE_GPU_FIRMWARE_LOGS, NV_REG_ENABLE_GPU_FIRMWARE_LOGS_ENABLE_ON_DEBUG);
 NV_DEFINE_REG_ENTRY(__NV_OPENRM_ENABLE_UNSUPPORTED_GPUS, 1);
+NV_DEFINE_REG_ENTRY(__NV_FORCE_EXTERNAL_GPU, 0);
 
 NV_DEFINE_REG_ENTRY_GLOBAL(__NV_ENABLE_USER_NUMA_MANAGEMENT, 1);
 NV_DEFINE_REG_ENTRY_GLOBAL(__NV_MEMORY_POOL_SIZE, 0);
@@ -1076,6 +1099,7 @@ nv_parm_t nv_parms[] = {
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_RM_NVLINK_BW_LINK_COUNT),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_ENABLE_DBG_BREAKPOINT),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_OPENRM_ENABLE_UNSUPPORTED_GPUS),
+    NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_FORCE_EXTERNAL_GPU),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_DMA_REMAP_PEER_MMIO),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_IMEX_CHANNEL_COUNT),
     NV_DEFINE_PARAMS_TABLE_ENTRY(__NV_CREATE_IMEX_CHANNEL_0),

src/nvidia/arch/nvalloc/unix/src/osinit.c

@@ -1310,10 +1310,29 @@ RmInitNvDevice(
     }
 
     // Configure eGPU setting
-    if (RmCheckForExternalGpu(pGpu, pCl))
     {
-        pGpu->setProperty(pGpu, PDB_PROP_GPU_IS_EXTERNAL_GPU, NV_TRUE);
-        nv->is_external_gpu = NV_TRUE;
+        NvU32 forceExternalGpu = 0;
+        NvBool isExternalGpu = NV_FALSE;
+
+        // Check if user has forced eGPU mode via module parameter
+        if ((osReadRegistryDword(pGpu, NV_REG_FORCE_EXTERNAL_GPU, &forceExternalGpu) == NV_OK) &&
+            (forceExternalGpu != 0))
+        {
+            NV_PRINTF(LEVEL_NOTICE, "Forcing external GPU mode via NVreg_ForceExternalGpu\n");
+            isExternalGpu = NV_TRUE;
+        }
+        else
+        {
+            // Otherwise, use automatic detection
+            isExternalGpu = RmCheckForExternalGpu(pGpu, pCl);
+        }
+
+        if (isExternalGpu)
+        {
+            NV_PRINTF(LEVEL_NOTICE, "GPU treated as external GPU (eGPU)\n");
+            pGpu->setProperty(pGpu, PDB_PROP_GPU_IS_EXTERNAL_GPU, NV_TRUE);
+            nv->is_external_gpu = NV_TRUE;
+        }
     }
     status->rmStatus = gpumgrStateInitGpu(pGpu);
     if (status->rmStatus != NV_OK)