STRUCT D40_CHAN(9)

💅 struct d40_chan(9) — the Kernel API Manual, but make it cute 🎀

okay so bestie, we're deep in the kernel API manual rn and this is struct d40_chan — literally the struct that describes a channel. yes, that kind of channel. sit down, grab a strawberry 🍓, and lemme walk you through every single field because there are a LOT and none of them are getting skipped.

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✨ NAME ✨

struct d40_chan — Struct that describes a channel. that's it, that's the whole name section, she's efficient 💅

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🌸 SYNOPSIS 🌸

struct d40_chan {
    spinlock_t lock;
    int log_num;
    int pending_tx;
    bool busy;
    struct d40_phy_res              *phy_chan;
    struct dma_chan                  chan;
    struct tasklet_struct            tasklet;
    struct list_head                 client;
    struct list_head                 pending_queue;
    struct list_head                 active;
    struct list_head                 done;
    struct list_head                 queue;
    struct list_head                 prepare_queue;
    struct stedma40_chan_cfg         dma_cfg;
    struct dma_slave_config          slave_config;
    bool configured;
    struct d40_base                 *base;
    u32 src_def_cfg;
    u32 dst_def_cfg;
    struct d40_def_lcsp              log_def;
    struct d40_log_lli_full         *lcpa;
    dma_addr_t runtime_addr;
    enum dma_transfer_direction     runtime_direction;
 };

look at her. twenty-two members. main character energy fr fr 👑

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🦋 Members 🦋

okay so this is the part where we go member by member, no skipping, no "etc." — every single one gets her moment:

• lock — a spinlock whose whole job is protecting this struct. she's the bodyguard, no cap 🫶
• log_num — the logical number of this channel, if there is one. "if any" — sometimes she's logged, sometimes she's mysterious 💅
• pending_tx — how many transfers are still pending. this one gets passed back and forth between the interrupt handler and the tasklet, like a group chat relay 🫡
• busy — gets set to true when a transfer is actively ongoing on this channel. she's booked and busy, literally 💀
• phy_chan — pointer to the physical channel this instance is running on. and heads up: if this pointer is NULL, then the channel isn't allocated. gone. not it. 🙈
• chan — the DMA engine handle. that's the vibe check for the DMA engine.
• tasklet — a tasklet that gets scheduled from interrupt context so it can complete a transfer and call the client callback. she's doing the follow-up work after the interrupt pops off 🔥
• client — the client-owned descriptor list. it's giving "your stuff, not mine" 🎀
• pending_queue — submitted jobs that are waiting to be issued by issue_pending. the queue before the queue, iykyk ✨
• active — the active descriptor. the one currently on stage 🌟
• done — completed jobs. the finished pile, iconic 👑
• queue — queued jobs. yes, there's also pending_queue and prepare_queue. three queues, three vibes, don't @ me 🌈
• prepare_queue — prepared jobs. she's prepping before she preps, that's the level of organization we stan
• dma_cfg — the client configuration of this dma channel
• slave_config — DMA slave configuration
• configured — whether the dma_cfg configuration is valid. a boolean of truth 💖
• base — pointer to the device instance struct
• src_def_cfg — default cfg register setting for src
• dst_def_cfg — default cfg register setting for dst
• log_def — default logical channel settings
• lcpa — pointer to the dst and src lcpa settings
• runtime_addr — the runtime configured address
• runtime_direction — the runtime configured direction

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💜 Description 💜

this struct can either "be" a logical channel or a physical channel — the quotes around "be" are doing a lot of heavy lifting here and honestly? she contains multitudes 🧚

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⭐ SEE ALSO ⭐

go read these, bestie, they're all in the kernel file ./drivers/dma/ste_dma40.c:

• struct stedma40_platform_data(9)
• enum d40_command(9)
• struct d40_interrupt_lookup(9)
• struct d40_reg_val(9)
• struct d40_lli_pool(9)
• struct d40_desc(9)
• struct d40_lcla_pool(9)
• struct d40_phy_res(9)
• struct d40_gen_dmac(9)
• struct d40_base(9)

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okay bestie that's the whole page, every single member accounted for, nothing dropped, we ate and left no crumbs 💅✨

and that's a wrap from ./drivers/dma, dated October 2026 — mwah, see you in the next manual page 🫶💖