vdma_desc_write_64(9)

📦 version 7.3.1, in nixpkgs unstable

💖 vdma_desc_write_64 — the Kernel API Manual, bestie edition 💖

okay so this is from the Kernel API Manual (yes, the (9) section, that's the kernel dev one, iykyk) and we're talking about vdma_desc_write_64(9). it's giving "tiny helper function that does one specific little thing and does it well." let's get into it 🎀

✨ NAME ✨

vdma_desc_write_64 — a 64-bit descriptor write. that's it. that's the whole vibe. 💅

🦋 SYNOPSIS 🦋

void vdma_desc_write_64 (struct xilinx_dma_chan *chan , u32 reg , u32
value_lsb , u32 value_msb );

like, she's a void function, she takes four things, she doesn't return anything because she doesn't need to ✨ (no notes, we love a low-maintenance icon)

🌸 ARGUMENTS 🌸

  • chan — the driver-specific VDMA channel 🫶 this is your channel, bestie, the one you're working with.
  • reg — the register to write. lowkey just tell her where to go.
  • value_lsb — the lower address of the descriptor 📥
  • value_msb — the upper address of the descriptor 📤

💜 DESCRIPTION 💜

okay so here's the situation, and it's kind of iconic honestly 😭

the vdma driver is trying to write to a register offset that is not a multiple of 64 bits — the manpage literally gives 0x5c as the example, and yeah, 0x5c is not it, she's just not 64-bit aligned, no cap 💀

so instead of doing a single 64-bit register write (which she simply cannot do at that offset), we write it as two separate 32-bit writes instead. that's the whole trick. split it up, send it in two,~~slay~~ done. it's giving "we made it work" energy and honestly? respect 🔥

fr fr this is a workaround-style behaviour, so don't go thinking you're getting one clean 64-bit write out here — you're getting two 32-bit pieces. periodt. 👑

⭐ SEE ALSO ⭐

a LOT of friends in this group chat, so buckle up bestie, we're tagging everybody 🎀

like I said. everybody. 🌈

🧚 sign-off 🧚

this little cutie lives in ./drivers/dma/xilinx 📁 and the page is dated October 2026 🗓️ — so yeah, she's from the future, main character energy only 👑✨ bye bestie, go write some descriptors 💖🦋

📦 where this page comes from