STRUCT HBM_DMA_RING_CTRL(9)

💅 struct hbm_dma_ring_ctrl — it's giving "dma ring control block"

okay so bestie, welcome to the Kernel API Manual section 9, and today's main character is struct hbm_dma_ring_ctrl, the dma ring control block 🎀 literally the little bookkeeping baddie that keeps track of where everybody is in the host and device circular buffers. no cap, it's just indexes and padding, but she ate.

✨ SYNOPSIS ✨

struct hbm_dma_ring_ctrl {
    u32 hbuf_wr_idx;
    u32 reserved1;
    u32 hbuf_rd_idx;
    u32 reserved2;
    u32 dbuf_wr_idx;
    u32 reserved3;
    u32 dbuf_rd_idx;
    u32 reserved4;
 };

like yes, it's a lot of u32s and a lot of reserveds — she's structured, she's aligned, she's iconic 🫶

🦋 Members 🦋

• hbuf_wr_idx — the host circular buffer write index, measured in slots ✍️
• reserved1 — reserved for alignment (padding princess, she's just here for the vibes 💅)
• hbuf_rd_idx — the host circular buffer read index, also in slots 👀
• reserved2 — reserved for alignment 🎀
• dbuf_wr_idx — the device circular buffer write index, in slots 🔥
• reserved3 — reserved for alignment ⭐
• dbuf_rd_idx — the device circular buffer read index, in slots 🌸
• reserved4 — reserved for alignment (last one, we love consistency 💜)

so the pattern is literally read/write index, then a lil alignment breather, then repeat for the device side. the reserved fields are only for alignment — don't be out here assigning meaning to them, bestie 😭

👑 SEE ALSO 👑

this is the part where the whole friend group shows up. from the kernel file ./drivers/misc/mei/hw.h, we've got:

• enum mei_hbm_status(9)
• enum mei_ext_hdr_type(9)
• struct mei_ext_hdr(9)
• struct mei_ext_meta_hdr(9)
• struct mei_ext_hdr_vtag(9)
• mei_ext_begin(9)
• mei_ext_last(9)
• struct mei_ext_hdr_gsc_h2f(9)
• struct mei_ext_hdr_gsc_f2h(9)
• mei_ext_next(9)
• mei_ext_hdr_len(9)
• struct mei_msg_hdr(9)
• struct mei_hbm_cl_cmd(9)
• enum hbm_host_enum_flags(9)
• struct hbm_host_enum_request(9)
• struct mei_client_properties(9)
• struct hbm_add_client_request(9)
• struct hbm_add_client_response(9)
• struct hbm_power_gate(9)
• struct hbm_client_connect_request(9)
• struct hbm_client_connect_response(9)
• struct hbm_notification_request(9)
• struct hbm_notification_response(9)
• struct hbm_notification(9)
• struct hbm_dma_mem_dscr(9)
• struct hbm_dma_setup_request(9)
• struct hbm_dma_setup_response(9)
• struct hbm_capability_request(9)
• struct hbm_capability_response(9)
• struct hbm_client_dma_map_request(9)
• struct hbm_client_dma_unmap_request(9)
• struct hbm_client_dma_response(9)

like, the whole squad fr fr 🌈 go read them, iykyk.

that's the whole page, periodt 💖 this came out of ./drivers/misc/mei, dated October 2026, and it's filed under struct hbm_dma_ring_ctrl(9) — mwah, slay, bye bestie 🧚🍓