STRUCT XE_GUC_CT(9)

🎀 struct xe_guc_ct(9)

okay bestie, buckle up — this is a page straight out of the Kernel API Manual, and it's all about struct xe_guc_ct, the GuC command transport (CT) layer. it's giving "the group chat between the Host and the GuC" and honestly? iconic. 💅

---

✨ SYNOPSIS ✨

struct xe_guc_ct {
    struct mutex lock;
    spinlock_t fast_lock;
    struct {
      struct guc_ctb h2g;
      struct guc_ctb g2h;
    } ctbs;
    u32 g2h_outstanding;
    struct work_struct g2h_worker;
    struct delayed_work safe_mode_worker;
    enum xe_guc_ct_state state;
    u32 fence_seqno;
    struct xarray fence_lookup;
    wait_queue_head_t wq;
    wait_queue_head_t g2h_fence_wq;
    struct workqueue_struct *g2h_wq;
    u32 msg[GUC_CTB_MSG_MAX_LEN];
    u32 fast_msg[GUC_CTB_MSG_MAX_LEN];
  #if IS_ENABLED(CONFIG_DRM_XE_DEBUG);
    struct xe_dead_ct dead;
    struct xe_fast_req_fence fast_req[SZ_32];
  #endif;
 };

like, look at her. she's got locks, she's got workqueues, she's got buffers. main character energy fr fr. 🌈

---

🌸 Members 🌸

time for the roll call, everyone say hi 👑

• lock — protects everything in CT layer. everything. she's the bodyguard of this whole struct, no cap.
• fast_lock — protects G2H channel and credits. the speedy little lock for the receive side ⚡
• ctbs — buffers for sending and receiving commands. the actual mailboxes, bestie 📬
  • ctbs.h2g — Host to GuC (H2G, send) channel — this is you sliding into GuC's DMs
  • ctbs.g2h — GuC to Host (G2H, receive) channel — and this is GuC replying back 💌
• g2h_outstanding — number of outstanding G2H. lowkey a counter of "how many texts are still on read" 😭
• g2h_worker — worker to process G2H messages. the one who actually goes through the inbox
• safe_mode_worker — worker to check G2H messages with IRQ disabled. careful mode ON, no interruptions allowed 🔥
• state — CT state. her current mood, basically.
• fence_seqno — G2H fence seqno - 16 bits used by CT. only 16 bits, so act accordingly 🎀
• fence_lookup — G2H fence lookup. the little index so you can find your fences again
• wq — wait queue used for reliable CT sends and freeing G2H credits. you wait here. patiently. 🫶
• g2h_fence_wq — wait queue used for G2H fencing. a second wait queue, because one is never enough
• g2h_wq — used to process G2H. the workqueue doing the actual processing
• msg — Message buffer. exactly what it says on the tin 💖
• fast_msg — Message buffer. the same thing, but fast ✨
• dead — information for debugging dead CTs 💀 yes the field is literally called dead, we love a dramatic queen
• fast_req — history of FAST_REQ messages for matching with G2H error responses. receipts, kept for later 🧾

---

🦋 Description 🦋

so what does she do? simple: this struct includes a pair of CT buffers for bi-directional communication 💫 plus all the tracking for the H2G and G2H requests sent and received through those buffers. two-way street, both directions monitored, everybody accounted for. periodt. 👑

---

⭐ SEE ALSO ⭐

go read these next, iykyk:

• Kernel file ./drivers/gpu/drm/xe/xe_guc_ct_types.h
• struct guc_ctb_info(9)
• struct guc_ctb(9)
• struct guc_ctb_snapshot(9)
• struct xe_guc_ct_snapshot(9)
• enum xe_guc_ct_state(9)

---

and that's the whole vibe check, bestie 🍓 this page lives in ./drivers/gpu/drm/xe, dated October 2026, and it's literally titled struct xe_guc_ct(9). go forth and ship it 💅💜