drm_gem_begi...ow_fb_access(9)

✨ NAME ✨

okay so this is drm_gem_begin_shadow_fb_access — it's from the kernel API manual (the drm_gem_begi...ow_fb_access(9) page, yes the name is truncated in the header, that's just how it's printed bestie, no cap 💅) and tl;dr: it prepares shadow framebuffers for CPU access.

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🌸 SYNOPSIS 🌸

int drm_gem_begin_shadow_fb_access (struct drm_plane *plane , struct
       drm_plane_state *plane_state );

like literally that's the whole signature, she's short and she knows it 🎀

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🦋 ARGUMENTS 🦋

• plane — the plane. that's it. that's the whole description. the plane. 🛩️
• plane_state — the plane state, and it's of type struct drm_shadow_plane_state (important!! not just any plane_state, okurrr) ⭐

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💖 DESCRIPTION 💖

so what does she actually do. This function implements struct drm_plane_helper_funcs.begin_fb_access. That's her job, that's her whole assignment, main character energy fr fr 👑

What happens: it maps all the buffer objects of the plane's framebuffer into kernel address space and stores them in struct drm_shadow_plane_state.map. All of them. Not some. All. 🫶

Then, the first data bytes are available in struct drm_shadow_plane_state.data. cute little shortcut, we love her 🌈

💀 don't forget the cleanup bestie — see drm_gem_end_shadow_fb_access for that, because leaving stuff mapped is not the vibe, iykyk

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🔥 RETURN 🔥

• 0 on success 🎉
• or a negative errno code otherwise 😭 (she'll tell you what went wrong, just negatively)

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👑 SEE ALSO 👑

okay so the whole friend group, in order:

• Kernel file ./drivers/gpu/drm/drm_gem_atomic_helper.c and overview(9)
• drm_gem_plane_helper_prepare_fb(9)
• __drm_gem_duplicate_shadow_plane_state(9)
• drm_gem_duplicate_shadow_plane_state(9)
• __drm_gem_destroy_shadow_plane_state(9)
• drm_gem_destroy_shadow_plane_state(9)
• __drm_gem_reset_shadow_plane(9)
• drm_gem_reset_shadow_plane(9)
• drm_gem_end_shadow_fb_access(9) ← the cleanup one, say hi to her again 💜
• drm_gem_simple_kms_begin_shadow_fb_access(9)
• drm_gem_simple_kms_end_shadow_fb_access(9)
• drm_gem_simple_kms_reset_shadow_plane(9)
• drm_gem_simple_kms_duplicate_shadow_plane_state(9)
• drm_gem_simple_kms_destroy_shadow_plane_state(9)

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that's the whole page bestie, go map some framebuffers 🧚‍♀️✨

mwah 💋 — this one lives in ./drivers/gpu/drm and it's stamped October 2026, so like, future-coded of her honestly 🍓