fsl_dma_hw_params(9)

📦 version 7.3.1, in nixpkgs unstable

💖 fsl_dma_hw_params — Kernel API Manual ✨

okay bestie, so this page is all about fsl_dma_hw_params(9) — that's the kernel API manual entry, the whole doc lives in the kernel API manual set, and we're about to get into it 🎀

🌸 NAME 🌸

fsl_dma_hw_params — continue initializing the DMA links ✨

🦋 SYNOPSIS 🦋

int fsl_dma_hw_params (struct snd_soc_component *component , struct
       snd_pcm_substream *substream , struct snd_pcm_hw_params *hw_params );

literally the whole signature up there, no notes 💅

💜 ARGUMENTS 💜

so the original is kinda shy about these, ngl. it says:

  • component — -- undescribed --
  • substream — -- undescribed --
  • hw_params — -- undescribed --

and that's it, that's the tea 🍵 like the manpage genuinely just leaves all three as "undescribed" so i'm not gonna sit here and make stuff up about them, iykyk 🙈

🔥 DESCRIPTION 🔥

okay so here's what it actually does: this function obtains hardware parameters about the opened stream and programs the DMA controller accordingly. icon behaviour honestly 👑

now, the main character energy of this whole page is the big-endian situation, so let's talk about it. one drawback of big-endian is that when you're copying integers of different sizes into a fixed-sized register, the address you have to copy the integer to depends on the size of the integer. the way that's kind of a whole thing 😭

for example — and this is the example straight from the page, keep up bestie:

  • if P is the address of a 32-bit register, and X is a 32-bit integer, then X should be copied to address P.
  • however, if X is a 16-bit integer, then it should be copied to P+2.
  • if X is an 8-bit register, then it should be copied to P+3.

so for playback of 8-bit samples, the DMA controller must transfer single bytes from the DMA buffer to the last byte of the STX0 register — i.e. offset by 3 bytes. for 16-bit samples, the offset is two bytes. 🫶

and for 24-bit samples, the offset is 1 byte. BUT — and this is the part where you gotta pay attention 🚨 — the DMA controller does not support 3-byte copies (the DAHTS register supports only 1, 2, 4, and 8 bytes at a time). so we do not support packed 24-bit samples. 24-bit data must be padded to 32 bits. periodt. no packed 24-bit for you, that's the rule 💀

fr fr do not try to sneak packed 24-bit samples past this thing — it's not a vibe, it's just not supported, the hardware genuinely can't do the 3-byte copy 🌸

🌈 SEE ALSO 🌈

go read the whole squad, they're all iconic in their own way 💖

and that's the page!! 🎀 this one lives under ./sound/soc/fsl in the kernel API manual, dated October 2026 — so yeah, future vibes, slay ⭐ bye bestie, go program that DMA controller responsibly 💅✨

📦 where this page comes from