Linux CXL 드라이버 분석 — cxl_pci·cxl_core·region·DAX

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drivers/cxl/
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├── Kconfig·Makefile
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├── acpi.c        — cxl_acpi: ACPI CEDT 파싱, root port 등록
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├── pci.c         — cxl_pci: PCI subsystem 통합, MMIO 매핑
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├── mem.c         — cxl_mem: memory device driver
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├── pmem.c        — cxl_pmem: persistent CXL
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├── port.c        — cxl_port: switch·root port driver
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└── core/         — cxl_core: 공통 베이스
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    ├── port.c    — CXL port·decoder 객체 관리
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    ├── region.c  — region 생성·관리
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    ├── memdev.c  — memory device 추상화
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    ├── hdm.c     — HDM Decoder 프로그래밍
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    ├── mbox.c    — Mailbox API
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    ├── regs.c    — register access helpers
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    └── pmem.c    — persistent memory 통합

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// drivers/cxl/pci.c (개념적, 단순화)
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static int cxl_pci_probe(struct pci_dev *pdev, ...)
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{
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    struct cxl_dev_state *cxlds;
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    // 1. CXL DVSEC 확인 (없으면 일반 PCI device로 처리)
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    if (!is_cxl_device(pdev))
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        return -ENODEV;
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    // 2. cxl_dev_state 할당 (모든 CXL 디바이스 공통 base)
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    cxlds = cxl_dev_state_create(&pdev->dev);
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    // 3. CXL MMIO BAR 매핑
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    rc = cxl_pci_setup_regs(pdev, cxlds);
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    // 4. Mailbox 초기화
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    rc = cxl_pci_setup_mailbox(cxlds);
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    // 5. CXL DVSEC capability 읽기
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    rc = cxl_dvsec_init(pdev, cxlds);
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    // 6. AER·RAS handler 등록
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    rc = cxl_pci_setup_aer(pdev);
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    // 7. memdev 등록 → cxl_mem 드라이버가 binding
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    rc = cxl_memdev_register(cxlds);
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    return 0;
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}

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// drivers/cxl/core/hdm.c (개념적)
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int cxl_decoder_commit(struct cxl_decoder *cxld)
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{
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    // 1. Decoder가 disable 상태인지 확인
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    if (cxld->flags & CXL_DECODER_F_ENABLE)
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        return -EBUSY;
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    // 2. 매핑할 SPA range 설정
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    write_mmio(cxld->base_lo, cxld->hpa_range.start & 0xFFFFFFFF);
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    write_mmio(cxld->base_hi, cxld->hpa_range.start >> 32);
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    write_mmio(cxld->size_lo, (cxld->size) & 0xFFFFFFFF);
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    write_mmio(cxld->size_hi, (cxld->size) >> 32);
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    // 3. Interleave 설정
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    write_mmio(cxld->control,
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        FIELD_PREP(CXL_DECODER_IW, cxld->interleave_ways) |
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        FIELD_PREP(CXL_DECODER_IG, cxld->interleave_granularity));
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    // 4. Decoder 활성화 (Commit)
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    set_bit(CXL_DECODER_F_ENABLE, &cxld->flags);
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    write_mmio(cxld->control, control_val | CXL_DECODER_ENABLE);
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    return 0;
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}

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// drivers/cxl/core/mbox.c (개념적)
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int cxl_mbox_send_cmd(struct cxl_dev_state *cxlds,
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                      u16 opcode,
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                      void *in_payload, size_t in_size,
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                      void *out_payload, size_t out_size)
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{
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    struct cxl_mbox_cmd mbox_cmd = {
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        .opcode = opcode,
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        .payload_in = in_payload,
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        .size_in = in_size,
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        .payload_out = out_payload,
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        .size_out = out_size,
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    };
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    // 1. Mailbox lock
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    mutex_lock(&cxlds->mbox_mutex);
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    // 2. Payload 작성
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    cxl_setup_mbox_cmd(cxlds, &mbox_cmd);
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    // 3. Command 보내기
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    write_mmio(cxlds->mbox_regs->command, opcode);
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    // 4. Response 기다림 (timeout 포함)
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    rc = wait_for_completion_timeout(&cxlds->mbox_done, MBOX_TIMEOUT_MS);
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    // 5. Result 읽기
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    if (rc > 0)
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        rc = cxl_read_mbox_response(cxlds, &mbox_cmd);
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    mutex_unlock(&cxlds->mbox_mutex);
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    return rc;
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}

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// drivers/cxl/core/region.c (개념적)
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static int cxl_region_attach(struct cxl_region *cxlr)
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{
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    // 1. SRAT 기반 또는 동적 노드 할당
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    int target_nid = cxl_region_pick_node(cxlr);
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    // 2. memory hot-add
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    rc = add_memory_driver_managed(target_nid, cxlr->res.start,
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                                    cxlr->res.end - cxlr->res.start,
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                                    "System RAM (CXL)",
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                                    MHP_MERGE_RESOURCE);
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    // 3. NUMA 노드 sysfs 등록
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    register_one_node(target_nid);
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    return 0;
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}

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// drivers/cxl/pci.c (개념적)
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static const struct pci_error_handlers cxl_pci_err_handlers = {
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    .error_detected = cxl_pci_error_detected,
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    .mmio_enabled = cxl_pci_mmio_enabled,
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    .slot_reset = cxl_pci_slot_reset,
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    .resume = cxl_pci_resume,
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    .cor_error_reported = cxl_cor_error_reported,
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};
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static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev, ...)
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{
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    struct cxl_dev_state *cxlds = pci_get_drvdata(pdev);
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    // 1. 에러 등급 분류
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    if (state == pci_channel_io_perm_failure) {
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        // Fatal — 디바이스 격리, region remove
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        cxl_memdev_set_offline(cxlds);
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        return PCI_ERS_RESULT_DISCONNECT;
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    }
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    // 2. AER 이벤트 처리
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    cxl_aer_handle(cxlds);
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    // 3. 권장 동작 return
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    return PCI_ERS_RESULT_NEED_RESET;
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}

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#define MBOX_TIMEOUT_MS 100   // 너무 짧음