dwc3_gadget...tx_fifo_size(9)

📦 version 7.3.1, in nixpkgs unstable

✨ dwc3_gadget...tx_fifo_size(9) ✨

okay bestie, so this page lives in the Kernel API Manual (yes the whole manual, we're fancy now 💅) and it's all about one little function that does fifo math so you don't have to. let's get into it 🫶

🌸 NAME 🌸

dwc3_gadget_calc_tx_fifo_size — the girlies that calculates the txfifo size value 💖 literally her whole job.

🎀 SYNOPSIS 🎀

int dwc3_gadget_calc_tx_fifo_size (struct dwc3 *dwc , int mult );

🦋 ARGUMENTS 🦋

  • dwc — pointer to the DWC3 context, aka the main character of this whole operation 👑
  • mult — the multiplier to be used when calculating the fifo_size, it's giving "how many times we're doing this" energy ✨

💜 DESCRIPTION 💜

So the way that this works is it calculates the size value based on the equation below, and the equation depends on which DWC3 revision you're on. v intentional, v specific:

DWC3 revision 280A and prior:

fifo_size = mult * (max_packet / mdwidth) + 1;

DWC3 revision 290A and onwards:

fifo_size = mult * ((max_packet + mdwidth)/mdwidth + 1) + 1

and bestie, the max packet size is set to 1024, because the txfifo requirements mainly apply to super speed USB use cases 🚀

ok but like — is overestimating a problem? no ma'am. it is safe to overestimate the fifo allocations for other scenarios, i.e. high speed USB. so we're just out here being generous with the fifo budget, no cap 🙈

🌈 SEE ALSO 🌈

the whole squad fr fr, all hanging out in the kernel file ./drivers/usb/dwc3/gadget.c:

ok that's the whole page bestie, mwah 💋 this one came from ./drivers/usb/dwc3, dated October 2026 — go forth and allocate your fifos responsibly, ily 🧚💜

📦 where this page comes from