amdgpu_ring_mux_get_rptr(9)

💅 amdgpu_ring_mux_get_rptr(9) — Kernel API Manual, but make it cute

okay so real talk, this is a page from the Kernel API Manual and honestly it's a little niche but we're gonna slay it anyway 🫶 it lives in the amdgpu world, and it's all about figuring out the readptr of a software ring. stay with me bestie, it's giving detective work 🔍✨

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🎀 NAME 🎀

amdgpu_ring_mux_get_rptr — get the readptr of the software ring. that's it, that's the whole vibe 💫

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🌸 SYNOPSIS 🌸

u64 amdgpu_ring_mux_get_rptr (struct amdgpu_ring_mux *mux , struct
amdgpu_ring *ring );

like, it takes a mux and a ring and hands you back a u64. iconic signature behavior 💅

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✨ ARGUMENTS ✨

• mux — the multiplexer that the software rings attach to 🧚 (yes, the rings are attached to it, it's a whole thing)
• ring — the software ring whose readptr we're calculating 🔥 that's the main character here

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🦋 DESCRIPTION 🦋

okay so listen 👀 the return value of the readptr is not precise while the other rings could write data onto the real ring buffer. and after overwriting on the real ring, we genuinely cannot decide if our packages have been executed or not read yet 😭 it's a whole mystery.

but wait — plot twist — this function is only called by tools such as umr to collect the latest packages for the hang analysis. so it's not out here doing everyday work, it's a specialist 🎀

and the working assumption is that the hang happens near our latest submit. so with that assumption locked in, we can use the following logic to give the clue:

• if the readptr is between start and end, then we return the copy pointer plus the distance from start to readptr 🌈
• if the readptr is before start, we return the copy pointer 💜
• lastly, if the readptr is past end, we return the write pointer 👑

three cases, three answers, no cap. it's giving "choose your own adventure" but for pointers 🦋

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💖 SEE ALSO 💖

• Kernel file ./drivers/gpu/drm/amd/amdgpu/amdgpu_ring_mux.c — go read the source bestie, it's right there 📖✨

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heads up: the imprecision is real and the man page says it plainly — this is a best-guess clue for hang analysis, not a precise readptr. don't come for me, I'm just the messenger 🫶

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and that's the whole page!! mwah 💋 this was brought to you by ./drivers/gpu/drm/amd/amdgpu, dated October 2026, all under the amdgpu_ring_mux_get_rptr(9) name — periodt, go forth and debug 🎀✨🌸