STRUCT MTU3_GPD_RING(9)

💖 struct mtu3_gpd_ring(9) 💖

okay so this is a page straight out of the Kernel API Manual, and it's all about struct mtu3_gpd_ring — the GPD ring descriptor. yes it's niche, yes it's USB, and yes we're gonna get into it. bestie, let's go 🫶

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✨ NAME ✨

struct mtu3_gpd_ring — the GPD ring descriptor, no cap. that's literally the whole name, and honestly? iconic.

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🌸 SYNOPSIS 🌸

struct mtu3_gpd_ring {
    dma_addr_t dma;
    struct qmu_gpd *start;
    struct qmu_gpd *end;
    struct qmu_gpd *enqueue;
    struct qmu_gpd *dequeue;
 };

five fields. that's the whole struct. short but it carries the entire ring energy 💅

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🎀 Members 🎀

the way each of these has a job and every single one of them is serving:

• dma — the physical base address of the GPD segment. the real-world address, the one the hardware actually knows about 💖
• start — the virtual base address of the GPD segment. the one we get to point at 🌸
• end — the last GPD element. that's the edge of the ring, bestie, the final boss 👑
• enqueue — the first empty GPD to use. where the next thing goes in ✨
• dequeue — the first completed GPD serviced by the ISR. where finished work comes back out 🦋

ngl the start/end + enqueue/dequeue duo is giving main character energy. two addresses, two pointers, one very tidy ring.

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💀 NOTE 💀

the size of GPD ring should be >= 2

fr fr, do not make it smaller than two. that's a requirement, not a suggestion 🙈

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🔥 SEE ALSO 🔥

everything else living in the neighbourhood — go read these too:

Kernel file ./drivers/usb/mtu3/mtu3.h

• enum mtu3_g_ep0_state(9)
• enum mtu3_dr_force_mode(9)
• struct mtu3_fifo_info(9)
• struct qmu_gpd(9)
• struct otg_switch_mtk(9)
• struct ssusb_mtk(9)
• struct mtu3_ep(9)
• struct mtu3(9)

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and that's the whole vibe check on struct mtu3_gpd_ring ⭐ this one came from ./drivers/usb/mtu3 (October 2026), so shoutout to the mtu3 directory and that date 🧚💜 periodt.