STRUCT BCM2835_SPI(9)

💖 struct bcm2835_spi — BCM2835 SPI controller 💖

okay so bestie, this is the kernel API manual page for struct bcm2835_spi(9), and it's lowkey one of those pages that looks like a giant struct but is actually just the BCM2835 SPI controller's whole personality in C form. no cap. ✨

🌸 NAME 🌸

struct bcm2835_spi — BCM2835 SPI controller. that's it, that's the vibe. 🎀

🦋 SYNOPSIS 🦋

struct bcm2835_spi {
    void __iomem *regs;
    struct clk *clk;
    struct gpio_desc *cs_gpio;
    unsigned long clk_hz;
    int irq;
    struct spi_transfer *tfr;
    struct spi_controller *ctlr;
    const u8 *tx_buf;
    u8 *rx_buf;
    int tx_len;
    int rx_len;
    int tx_prologue;
    int rx_prologue;
    unsigned int tx_spillover;
    struct dentry *debugfs_dir;
    u64 count_transfer_polling;
    u64 count_transfer_irq;
    u64 count_transfer_irq_after_polling;
    u64 count_transfer_dma;
    struct bcm2835_spidev *target;
    unsigned int tx_dma_active;
    unsigned int rx_dma_active;
    struct dma_async_tx_descriptor *fill_tx_desc;
    dma_addr_t fill_tx_addr;
};

she's giving "struct with lore" and honestly? obsessed. 💅

🎀 Members 🎀

• regs — base address of the register map. the home base, the main character location. 🗺️
• clk — the core clock, divided to calculate the serial clock. math but make it sparkly. ✨
• cs_gpio — chip-select GPIO descriptor. it's the little handle that says "this one, bestie." 🫶
• clk_hz — the core clock's cached speed. cached, so we don't have to keep asking. 💅
• irq — the interrupt; it signals when TX FIFO is empty or RX FIFO is ¾ full. yes, exactly ¾, not 3/4 casually — the manual said ¾ and we respect it. 😭
• tfr — the SPI transfer currently being processed. current hyperfixation, basically. 🔥
• ctlr — SPI controller reverse lookup. like finding the controller's insta from its @ handle. 🔍
• tx_buf — pointer where the next transmitted byte is read from. the outgoing mail slot. 📤
• rx_buf — pointer where the next received byte is written. the incoming mail slot. 📥
• tx_len — remaining bytes to transmit. how much yapping is left, in bytes. 🗣️
• rx_len — remaining bytes to receive. how much listening is left, in bytes. 👂
• tx_prologue — bytes transmitted without DMA if the first TX sglist entry's length is not a multiple of 4 (to overcome a hardware limitation). not me fixing the hardware's little quirk with a prologue. 🧚
• rx_prologue — bytes received without DMA if the first RX sglist entry's length is not a multiple of 4 (to overcome a hardware limitation). same energy, receive edition. 🦋
• tx_spillover — whether tx_prologue spills over into the second TX sglist entry. spill the tea, but like, into the next sglist entry. 🍓
• debugfs_dir — the debugfs directory — neede to remove debugfs when unloading the module. yes bestie, "neede" is literally what the source says, and honestly? relatable typo. 💀
• count_transfer_polling — count of how often polling mode is used. keeping receipts on polling. 🧾
• count_transfer_irq — count of how often interrupt mode is used. keeping receipts on interrupts too. 🔥
• count_transfer_irq_after_polling — count of how often we fall back to interrupt mode after starting in polling mode. and these are counted as well in count_transfer_polling and count_transfer_irq — yes, double-counted, it's giving "counted twice because the vibes require it." 😭
• count_transfer_dma — count how often DMA mode is used. DMA receipt-keeping: activated. 💅
• target — SPI target currently selected (used by bcm2835_spi_dma_tx_done to write clear_rx_cs). the chosen one, iykyk. 👑
• tx_dma_active — whether a TX DMA descriptor is in progress. is TX DMA active? the field says yes/no. iconic. 🎀
• rx_dma_active — whether a RX DMA descriptor is in progress (used by bcm2835_spi_dma_tx_done to handle a race). yes, there's a race, and this field is the little referee. 🏁
• fill_tx_desc — a preallocated TX DMA descriptor used for RX-only transfers (it cyclically copies from zero page to TX FIFO). zero page to TX FIFO on loop, like a playlist you put on repeat. 🔁
• fill_tx_addr — bus address of zero page. the address of the zero page, bestie. that's the fact. 🫶

💫 SEE ALSO 💫

• Kernel file ./drivers/spi/spi-bcm2835.c
• struct bcm2835_spidev(9)
• bcm2835_rd_fifo_count(9)
• bcm2835_wr_fifo_count(9)
• bcm2835_wait_tx_fifo_empty(9)
• bcm2835_rd_fifo_blind(9)
• bcm2835_wr_fifo_blind(9)
• bcm2835_spi_transfer_prologue(9)
• bcm2835_spi_undo_prologue(9)
• bcm2835_spi_dma_rx_done(9)
• bcm2835_spi_dma_tx_done(9)
• bcm2835_spi_prepare_sg(9)
• bcm2835_spi_transfer_one_dma(9)

and that's the page, bestie. this little baddie lives at source ./drivers/spi and is dated October 2026 — screenshot it, cite it, slay it. 💖✨🎀🦋🌸💅🫶