1.. SPDX-License-Identifier: GPL-2.0 2 3================ 4fwctl cxl driver 5================ 6 7:Author: Dave Jiang 8 9Overview 10======== 11 12The CXL spec defines a set of commands that can be issued to the mailbox of a 13CXL device or switch. It also left room for vendor specific commands to be 14issued to the mailbox as well. fwctl provides a path to issue a set of allowed 15mailbox commands from user space to the device moderated by the kernel driver. 16 17The following 3 commands will be used to support CXL Features: 18CXL spec r3.1 8.2.9.6.1 Get Supported Features (Opcode 0500h) 19CXL spec r3.1 8.2.9.6.2 Get Feature (Opcode 0501h) 20CXL spec r3.1 8.2.9.6.3 Set Feature (Opcode 0502h) 21 22The "Get Supported Features" return data may be filtered by the kernel driver to 23drop any features that are forbidden by the kernel or being exclusively used by 24the kernel. The driver will set the "Set Feature Size" of the "Get Supported 25Features Supported Feature Entry" to 0 to indicate that the Feature cannot be 26modified. The "Get Supported Features" command and the "Get Features" falls 27under the fwctl policy of FWCTL_RPC_CONFIGURATION. 28 29For "Set Feature" command, the access policy currently is broken down into two 30categories depending on the Set Feature effects reported by the device. If the 31Set Feature will cause immediate change to the device, the fwctl access policy 32must be FWCTL_RPC_DEBUG_WRITE_FULL. The effects for this level are 33"immediate config change", "immediate data change", "immediate policy change", 34or "immediate log change" for the set effects mask. If the effects are "config 35change with cold reset" or "config change with conventional reset", then the 36fwctl access policy must be FWCTL_RPC_DEBUG_WRITE or higher. 37 38fwctl cxl User API 39================== 40 41.. kernel-doc:: include/uapi/fwctl/cxl.h 42 431. Driver info query 44-------------------- 45 46First step for the app is to issue the ioctl(FWCTL_CMD_INFO). Successful 47invocation of the ioctl implies the Features capability is operational and 48returns an all zeros 32bit payload. A ``struct fwctl_info`` needs to be filled 49out with the ``fwctl_info.out_device_type`` set to ``FWCTL_DEVICE_TYPE_CXL``. 50The return data should be ``struct fwctl_info_cxl`` that contains a reserved 5132bit field that should be all zeros. 52 532. Send hardware commands 54------------------------- 55 56Next step is to send the 'Get Supported Features' command to the driver from 57user space via ioctl(FWCTL_RPC). A ``struct fwctl_rpc_cxl`` is pointed to 58by ``fwctl_rpc.in``. ``struct fwctl_rpc_cxl.in_payload`` points to 59the hardware input structure that is defined by the CXL spec. ``fwctl_rpc.out`` 60points to the buffer that contains a ``struct fwctl_rpc_cxl_out`` that includes 61the hardware output data inlined as ``fwctl_rpc_cxl_out.payload``. This command 62is called twice. First time to retrieve the number of features supported. 63A second time to retrieve the specific feature details as the output data. 64 65After getting the specific feature details, a Get/Set Feature command can be 66appropriately programmed and sent. For a "Set Feature" command, the retrieved 67feature info contains an effects field that details the resulting 68"Set Feature" command will trigger. That will inform the user whether 69the system is configured to allowed the "Set Feature" command or not. 70 71Code example of a Get Feature 72~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 73 74.. code-block:: c 75 76 static int cxl_fwctl_rpc_get_test_feature(int fd, struct test_feature *feat_ctx, 77 const uint32_t expected_data) 78 { 79 struct cxl_mbox_get_feat_in *feat_in; 80 struct fwctl_rpc_cxl_out *out; 81 struct fwctl_rpc rpc = {0}; 82 struct fwctl_rpc_cxl *in; 83 size_t out_size, in_size; 84 uint32_t val; 85 void *data; 86 int rc; 87 88 in_size = sizeof(*in) + sizeof(*feat_in); 89 rc = posix_memalign((void **)&in, 16, in_size); 90 if (rc) 91 return -ENOMEM; 92 memset(in, 0, in_size); 93 feat_in = &in->get_feat_in; 94 95 uuid_copy(feat_in->uuid, feat_ctx->uuid); 96 feat_in->count = feat_ctx->get_size; 97 98 out_size = sizeof(*out) + feat_ctx->get_size; 99 rc = posix_memalign((void **)&out, 16, out_size); 100 if (rc) 101 goto free_in; 102 memset(out, 0, out_size); 103 104 in->opcode = CXL_MBOX_OPCODE_GET_FEATURE; 105 in->op_size = sizeof(*feat_in); 106 107 rpc.size = sizeof(rpc); 108 rpc.scope = FWCTL_RPC_CONFIGURATION; 109 rpc.in_len = in_size; 110 rpc.out_len = out_size; 111 rpc.in = (uint64_t)(uint64_t *)in; 112 rpc.out = (uint64_t)(uint64_t *)out; 113 114 rc = send_command(fd, &rpc, out); 115 if (rc) 116 goto free_all; 117 118 data = out->payload; 119 val = le32toh(*(__le32 *)data); 120 if (memcmp(&val, &expected_data, sizeof(val)) != 0) { 121 rc = -ENXIO; 122 goto free_all; 123 } 124 125 free_all: 126 free(out); 127 free_in: 128 free(in); 129 return rc; 130 } 131 132Take a look at CXL CLI test directory 133<https://github.com/pmem/ndctl/tree/main/test/fwctl.c> for a detailed user code 134for examples on how to exercise this path. 135 136 137fwctl cxl Kernel API 138==================== 139 140.. kernel-doc:: drivers/cxl/core/features.c 141 :export: 142.. kernel-doc:: include/cxl/features.h 143