STRUCT DMA_ASYNC_TX_DESCRIPTOR(9)

✨ struct dma_async_tx_descriptor(9) ✨

okay so this is from the Kernel API Manual bestie, and it's literally the blueprint for struct dma_async_tx_descriptor — the async transaction descriptor, aka the dma generic offload fields situation. iykyk 💅

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🦋 NAME 🦋

struct dma_async_tx_descriptor — async transaction descriptor ---dma generic offload fields---

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🎀 SYNOPSIS 🎀

struct dma_async_tx_descriptor {
    dma_cookie_t cookie;
    enum dma_ctrl_flags flags;
    dma_addr_t phys;
    struct dma_chan *chan;
    dma_cookie_t (*tx_submit)(struct dma_async_tx_descriptor *tx);
    int (*desc_free)(struct dma_async_tx_descriptor *tx);
    dma_async_tx_callback callback;
    dma_async_tx_callback_result callback_result;
    void *callback_param;
    struct dmaengine_unmap_data *unmap;
    enum dma_desc_metadata_mode desc_metadata_mode;
    const struct dma_descriptor_metadata_ops *metadata_ops;
  #ifdef CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH;
    struct dma_async_tx_descriptor *next;
    struct dma_async_tx_descriptor *parent;
    spinlock_t lock;
  #endif;
 };

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🌸 Members 🌸

okay so first up we have the dma generic offload fields era of the struct — the core squad 🫶

• cookie — the tracking cookie for this transaction, bestie 🍪 and plot twist: it's set to -EBUSY if this tx is sitting on a dependency list. like it's literally occupied, leave her alone.
• flags — flags that augment operation preparation, control completion, and communicate status. the whole vibe-control department ✨
• phys — physical address of the descriptor. that's her real address, no catfishing 📍
• chan — target channel for this operation. where the work actually gets sent 💌
• tx_submit — accept the descriptor, assign an ordered cookie, and mark the descriptor pending. To be pushed on .issue_pending call. she's queued and ready, no cap 🔥
• desc_free — the driver's callback function to free a resusable descriptor after completion. cleanup crew, iconic 🧹
• callback — routine to call after this operation is complete. the "we're so back" moment 💖
• callback_result — error result from a DMA transaction. receipts, basically 😭
• callback_param — general parameter to pass to the callback routine. lil extra to hand over 🎁
• unmap — hook for generic DMA unmap data. the un-hook, if you will 🪝
• desc_metadata_mode — core managed metadata mode, and the whole point is to protect mixed use of DESC_METADATA_CLIENT or DESC_METADATA_ENGINE. Otherwise it's DESC_METADATA_NONE. pick a lane bestie 💀
• metadata_ops — DMA driver provided metadata mode ops, and these need to be set by the DMA driver if metadata mode is supported with the descriptor. no ops, no metadata party 🙈

⭐ async_tx api specific fields ⭐

now the async_tx api specific fields section, the dependency-chain girlies 👑

• next — at completion, submit this descriptor. the "and then??" energy ⏭️
• parent — pointer to the next level up in the dependency chain. mother is mothering 👑
• lock — protect the parent and next pointers. do not touch without the lock, i'm serious 🫶

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🌈 SEE ALSO 🌈

Kernel file ./include/linux/dmaengine.h — the source of truth, go read her 📖

• dma_cookie_t(9)
• enum dma_status(9)
• enum dma_transaction_type(9)
• enum dma_transfer_direction(9)
• struct data_chunk(9)
• struct dma_interleaved_template(9)
• struct dma_vec(9)
• enum dma_ctrl_flags(9)
• enum sum_check_bits(9)
• enum sum_check_flags(9)
• enum dma_desc_metadata_mode(9)
• struct dma_chan_percpu(9)
• struct dma_router(9)
• struct dma_chan(9)
• struct dma_chan_dev(9)
• enum dma_slave_buswidth(9)
• struct dma_slave_config(9)
• enum dma_residue_granularity(9)
• struct dma_slave_caps(9)
• dma_filter_fn(9)
• struct dma_tx_state(9)
• enum dmaengine_alignment(9)
• struct dma_slave_map(9)
• struct dma_filter(9)
• struct dma_device(9)
• dmaengine_prep_peripheral_dma_vec(9)
• dmaengine_prep_config_sg_safe(9)
• dmaengine_prep_config_single_safe(9)
• dmaengine_prep_dma_memset(9)
• dmaengine_terminate_all(9)
• dmaengine_terminate_async(9)
• dmaengine_synchronize(9)
• dmaengine_terminate_sync(9)
• dma_async_issue_pending(9)
• dma_async_is_tx_complete(9)
• dma_async_is_complete(9)

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and that's the whole page bestie, we ate and left no crumbs 💅✨

🌸 signed, sealed, delivered from ./include/linux with a date stamp of October 2026 — struct dma_a...x_descriptor(9) forever and always 🎀🦋💜