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Diffstat (limited to 'Documentation/userspace-api/fwctl/fwctl-cxl.rst')
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diff --git a/Documentation/userspace-api/fwctl/fwctl-cxl.rst b/Documentation/userspace-api/fwctl/fwctl-cxl.rst new file mode 100644 index 000000000000..670b43b72949 --- /dev/null +++ b/Documentation/userspace-api/fwctl/fwctl-cxl.rst @@ -0,0 +1,142 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================ +fwctl cxl driver +================ + +:Author: Dave Jiang + +Overview +======== + +The CXL spec defines a set of commands that can be issued to the mailbox of a +CXL device or switch. It also left room for vendor specific commands to be +issued to the mailbox as well. fwctl provides a path to issue a set of allowed +mailbox commands from user space to the device moderated by the kernel driver. + +The following 3 commands will be used to support CXL Features: +CXL spec r3.1 8.2.9.6.1 Get Supported Features (Opcode 0500h) +CXL spec r3.1 8.2.9.6.2 Get Feature (Opcode 0501h) +CXL spec r3.1 8.2.9.6.3 Set Feature (Opcode 0502h) + +The "Get Supported Features" return data may be filtered by the kernel driver to +drop any features that are forbidden by the kernel or being exclusively used by +the kernel. The driver will set the "Set Feature Size" of the "Get Supported +Features Supported Feature Entry" to 0 to indicate that the Feature cannot be +modified. The "Get Supported Features" command and the "Get Features" falls +under the fwctl policy of FWCTL_RPC_CONFIGURATION. + +For "Set Feature" command, the access policy currently is broken down into two +categories depending on the Set Feature effects reported by the device. If the +Set Feature will cause immediate change to the device, the fwctl access policy +must be FWCTL_RPC_DEBUG_WRITE_FULL. The effects for this level are +"immediate config change", "immediate data change", "immediate policy change", +or "immediate log change" for the set effects mask. If the effects are "config +change with cold reset" or "config change with conventional reset", then the +fwctl access policy must be FWCTL_RPC_DEBUG_WRITE or higher. + +fwctl cxl User API +================== + +.. kernel-doc:: include/uapi/fwctl/cxl.h + +1. Driver info query +-------------------- + +First step for the app is to issue the ioctl(FWCTL_CMD_INFO). Successful +invocation of the ioctl implies the Features capability is operational and +returns an all zeros 32bit payload. A ``struct fwctl_info`` needs to be filled +out with the ``fwctl_info.out_device_type`` set to ``FWCTL_DEVICE_TYPE_CXL``. +The return data should be ``struct fwctl_info_cxl`` that contains a reserved +32bit field that should be all zeros. + +2. Send hardware commands +------------------------- + +Next step is to send the 'Get Supported Features' command to the driver from +user space via ioctl(FWCTL_RPC). A ``struct fwctl_rpc_cxl`` is pointed to +by ``fwctl_rpc.in``. ``struct fwctl_rpc_cxl.in_payload`` points to +the hardware input structure that is defined by the CXL spec. ``fwctl_rpc.out`` +points to the buffer that contains a ``struct fwctl_rpc_cxl_out`` that includes +the hardware output data inlined as ``fwctl_rpc_cxl_out.payload``. This command +is called twice. First time to retrieve the number of features supported. +A second time to retrieve the specific feature details as the output data. + +After getting the specific feature details, a Get/Set Feature command can be +appropriately programmed and sent. For a "Set Feature" command, the retrieved +feature info contains an effects field that details the resulting +"Set Feature" command will trigger. That will inform the user whether +the system is configured to allowed the "Set Feature" command or not. + +Code example of a Get Feature +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + static int cxl_fwctl_rpc_get_test_feature(int fd, struct test_feature *feat_ctx, + const uint32_t expected_data) + { + struct cxl_mbox_get_feat_in *feat_in; + struct fwctl_rpc_cxl_out *out; + struct fwctl_rpc rpc = {0}; + struct fwctl_rpc_cxl *in; + size_t out_size, in_size; + uint32_t val; + void *data; + int rc; + + in_size = sizeof(*in) + sizeof(*feat_in); + rc = posix_memalign((void **)&in, 16, in_size); + if (rc) + return -ENOMEM; + memset(in, 0, in_size); + feat_in = &in->get_feat_in; + + uuid_copy(feat_in->uuid, feat_ctx->uuid); + feat_in->count = feat_ctx->get_size; + + out_size = sizeof(*out) + feat_ctx->get_size; + rc = posix_memalign((void **)&out, 16, out_size); + if (rc) + goto free_in; + memset(out, 0, out_size); + + in->opcode = CXL_MBOX_OPCODE_GET_FEATURE; + in->op_size = sizeof(*feat_in); + + rpc.size = sizeof(rpc); + rpc.scope = FWCTL_RPC_CONFIGURATION; + rpc.in_len = in_size; + rpc.out_len = out_size; + rpc.in = (uint64_t)(uint64_t *)in; + rpc.out = (uint64_t)(uint64_t *)out; + + rc = send_command(fd, &rpc, out); + if (rc) + goto free_all; + + data = out->payload; + val = le32toh(*(__le32 *)data); + if (memcmp(&val, &expected_data, sizeof(val)) != 0) { + rc = -ENXIO; + goto free_all; + } + + free_all: + free(out); + free_in: + free(in); + return rc; + } + +Take a look at CXL CLI test directory +<https://github.com/pmem/ndctl/tree/main/test/fwctl.c> for a detailed user code +for examples on how to exercise this path. + + +fwctl cxl Kernel API +==================== + +.. kernel-doc:: drivers/cxl/core/features.c + :export: +.. kernel-doc:: include/cxl/features.h |