STRUCT DRM_ASAHI_CMD_HEADER(9)

💅 struct drm_asahi_cmd_header(9) — Kernel API Manual 🎀

okay so bestie, this is the <cyan>kernel API manual</cyan> page for struct drm_asahi_cmd_header, and honestly? it's kind of the main character of the whole command buffer situation. let's get into it ✨

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🌸 NAME 🌸

struct drm_asahi_cmd_header — the top level command structure, fr fr. it's the header that sits on top of your commands like a little crown 👑

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✨ SYNOPSIS ✨

struct drm_asahi_cmd_header {
    __u16 cmd_type;
    __u16 size;
    __u16 vdm_barrier;
    __u16 cdm_barrier;
 };

that's it. four fields. tiny. iconic. 🫶

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🎀 Members 🎀

💜 cmd_type

one of drm_asahi_cmd_type — like, pick your fighter, bestie 💅

🦋 size

the size of this command, not including this header. so don't count the header itself, that's a whole separate vibe.

for hardware commands, this is what lets commands be extensible without needing a million extra command types. and here's the slay part: passing a command that's shorter than expected is explicitly allowed for backwards-compatibility. truncated fields just get zeroed. no drama, no cap 🙈

for the synthetic attachment setting commands, this implicitly encodes the number of attachments. those commands take multiple fixed-size drm_asahi_attachment structures as their payload, so:

size equals number of attachments * sizeof(struct drm_asahi_attachment)

math queen behavior, honestly 🧮👑

🌈 vdm_barrier

VDM (render) command index to wait on. it's giving "hold up, let them go first" energy.

so how do barriers work? they're indices relative to the beginning of a given submit. let me break it down:

• a barrier of 0 waits on commands submitted to the respective subqueue in previous submit ioctls
• a barrier of N waits on N previous commands on the subqueue within the current submit ioctl
• and as a special case, passing DRM_ASAHI_BARRIER_NONE avoids waiting on any commands in the subqueue ⭐

⭐ Examples ⭐

• 0: this waits on all previous work. all of it. patient queen 💅
• NONE: this does not wait for anything on this subqueue. zero thoughts, head empty 🫧
• 1: this waits on the first render command in the submit. this is valid only if there are multiple render commands in the same submit 👀

barriers are valid only for hardware commands. synthetic software commands to set attachments must pass NONE here. no exceptions, bestie. periodt. 🔥

🍓 cdm_barrier

CDM (compute) command index to wait on.

just see vdm_barrier, and replace VDM/render with CDM/compute. same energy, different subqueue, iykyk 💖

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👑 Description 👑

this struct is core to the command buffer definition and therefore is not extensible.

like, it's the blueprint. it's not getting new features. it's done. it's retired. we respect it 😌🌸

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🌟 SEE ALSO 🌟

• Kernel file ./include/uapi/drm/asahi_drm.h
• Introduction to the Asahi UAPI(9)
• enum drm_asahi_ioctl_id(9)
• struct drm_asahi_params_global(9)
• enum drm_asahi_feature(9)
• struct drm_asahi_get_params(9)
• struct drm_asahi_vm_create(9)
• struct drm_asahi_vm_destroy(9)
• enum drm_asahi_gem_flags(9)
• struct drm_asahi_gem_create(9)
• struct drm_asahi_gem_mmap_offset(9)
• enum drm_asahi_bind_flags(9)
• struct drm_asahi_gem_bind_op(9)
• struct drm_asahi_vm_bind(9)
• enum drm_asahi_bind_object_op(9)
• enum drm_asahi_bind_object_flags(9)
• struct drm_asahi_gem_bind_object(9)
• enum drm_asahi_cmd_type(9)
• enum drm_asahi_priority(9)
• struct drm_asahi_queue_create(9)
• struct drm_asahi_queue_destroy(9)
• enum drm_asahi_sync_type(9)
• struct drm_asahi_sync(9)
• DRM_ASAHI_BARRIER_NONE(9)
• struct drm_asahi_submit(9)
• struct drm_asahi_attachment(9)
• struct drm_asahi_zls_buffer(9)
• struct drm_asahi_timestamp(9)
• struct drm_asahi_timestamps(9)
• struct drm_asahi_helper_program(9)
• struct drm_asahi_bg_eot(9)
• struct drm_asahi_cmd_render(9)
• struct drm_asahi_cmd_compute(9)
• struct drm_asahi_get_time(9)
• DRM_IOCTL_ASAHI(9)

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and that's the whole page, bestie! 🎀 this one lives in ./include/uapi/drm and it's dated October 2026 — go read the whole Asahi UAPI saga, it ate and left no crumbs 💅✨🦋