iosf_mbi_punit_acquire(9)

💅 iosf_mbi_punit_acquire(9) — like, the Kernel API Manual era 🎀

okay bestie, buckle up, because this one is a kernel function name so long it's practically a whole personality. It lives in the Kernel API Manual, and yes, we're getting into it.

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✨ NAME ✨

iosf_mbi_punit_acquire — the function that politely but firmly says "mine now" and acquires access to the P-Unit 🫶

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🌸 SYNOPSIS 🌸

void iosf_mbi_punit_acquire (void );

literally that's it. that's the whole call.

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🦋 ARGUMENTS 🦋

• void — no arguments. zero. zilch. nothing to pass in, nothing to get wrong. iconic behaviour honestly 👑

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💖 DESCRIPTION 💖

so on some systems, the P-Unit goes and accesses the PMIC to change various voltages — and it does that through the same bus that other kernel drivers use for stuff like battery monitoring. shared bus. shared vibes. what could possibly go wrong 💀

and here's the thing, bestie: if a driver sends requests to the P-Unit that require the P-Unit to hit the PMIC bus while another driver is also accessing the PMIC bus, various bad things happen. not like, cute bad. bad bad. 😭

so the move is: call this function before sending requests to the P-Unit that may make it access the PMIC — whether that's through iosf_mbi* functions or through other means. no exceptions, no "it'll probably be fine". this function will block all kernel access to the PMIC I2C bus so the P-Unit can safely access the PMIC over that shared I2C bus. it's giving traffic cop. it's giving bouncer at the club. 🚦

now, a note on these systems: the i2c-bus driver will request a semaphore from the P-Unit for exclusive access to the PMIC bus when i2c drivers are accessing it — but ngl, that does not appear to be sufficient. we still need to avoid making certain P-Unit requests during the access window to avoid problems. so like, the semaphore is not the whole story, periodt.

⚠️ heads up: this function locks a mutex, which means it may sleep. do not come for it with your atomic-context nonsense, it will not be slayed by that. 🙈

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🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/include/asm/iosf_mbi.h
• iosf_mbi_read(9)
• iosf_mbi_write(9)
• iosf_mbi_modify(9)
• iosf_mbi_punit_release(9)
• iosf_mbi_block_punit_i2c_access(9)
• iosf_mbi_register_pmic_bus_access_notifier(9)
• iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(9)
• iosf_mbi_assert_punit_acquired(9)

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aaaand that's the page, bestie 💜 this lil beauty comes to you from ./arch/x86/include/asm and it's dated October 2026 — so yeah, it's from the future, main character energy fr fr ✨🦋🎀