ahci_mvebu_stop_engine(9)

✨ ahci_mvebu_stop_engine 💅

okay so this is a page from the Kernel API Manual, bestie, and it's about one very specific little function that exists purely to babysit some hardware that misbehaves 🫶

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🌸 NAME 🌸

ahci_mvebu_stop_engine — literally just the name, that's it, the original page gives us no one-liner here, so we're not making one up 💀 (iconic of it, honestly)

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🎀 SYNOPSIS 🎀

int ahci_mvebu_stop_engine (struct ata_port *ap );

that's the whole vibe check: it takes a pointer to a struct ata_port and hands you back an int ✨

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🦋 ARGUMENTS 🦋

• ap — the target ata port 🎯 that's the one, that's the port we're doing surgery on

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💖 DESCRIPTION 💖

okay so gather round because this is the whole lore 👑

Errata Ref#226 — a SATA Disk HOT swap issue that happens when the disk is connected through a Port Multiplier in FIS-based Switching mode 😭 like that's the bug, that's the cursed situation.

so the way the hardware is designed (according to design, not according to us), to dodge this issue: the bits [11:8, 0] of register PxFBS get cleared when Port Command and Status (0x18) bit [0] changes its value from 1 to 0 🫠 iykyk — that's the falling edge of Port Command and Status bit [0], and that falling edge sends a PULSE that resets PxFBS bits [11:8; 0] ⚡ so yeah. the register just gets yeeted back to zero on you.

and this function? this function is the workaround bestie 💅 it overrides the function "ahci_stop_engine" from libahci.c by adding the mvebu work around (WA), and the WA does exactly two things:

1. save the PxFBS value before the PxCMD ST write of 0 🙈
2. restore the PxFBS value afterwards ✨

so the bits survive the pulse. ate. no cap 💜

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🔥 RETURN 🔥

• 0 on success 🎉
• Error code otherwise 😭 (so like, check it, fr fr)

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🌈 SEE ALSO 🌈

• Kernel file ./drivers/ata/ahci_mvebu.c 👀 go read the source, it's giving main character energy

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⭐ friendly reminder from your girl: this is a workaround, so if you're touching it, know that you're dealing with errata behaviour and a hardware pulse that resets register bits. don't get cute with it 💀

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okay that's the page!! 🍓 this was ahci_mvebu_stop_engine(9) from the Kernel API Manual, filed under ./drivers/ata, dated October 2026 — mwah, love ya, go stop some engines 💅💖🧚