sdio_readw(9)

📦 version 7.3.1, in nixpkgs unstable

💖 sdio_readw — bestie edition 💖

okay so real talk, this one lives in the Kernel API Manual and it's literally just "read a 16 bit integer from a SDIO function" and honestly? iconic. tiny little function, does exactly one thing, slays. 🎀

✨ SYNOPSIS ✨

u16 sdio_readw (struct sdio_func *func , unsigned int addr , int
*err_ret );

like, that's the whole vibe. three args, one u16 coming back at you. 💅

🌸 ARGUMENTS 🌸

  • func — the SDIO function you wanna access. your main character. the one you're talking to. 🫶
  • addr — the address you're reading from. yes bestie, this exact one, no cap. 📍
  • err_ret — optional status value from the transfer. it's optional so like, you can pass NULL, but then you're reading on hard mode ngl. 🙈

🦋 DESCRIPTION 🦋

So the way this works: sdio_readw reads a 16 bit integer out of the address space of a given SDIO function. that's it, that's the whole job, and it eats every time. ✨

BUT — and this is the important part, listen to me — if there's a problem reading the address, it returns 0xffff and err_ret will contain the error code. so like, if you get 0xffff back, don't just assume the hardware said 0xffff?? check err_ret first, fr fr. that's your vibe check. 😭💀

ngl this is the kind of thing that bites you at 3am. 0xffff is both a valid-looking number AND the error sentinel, so please please please actually read err_ret. 🧚

👑 SEE ALSO 👑

Kernel file ./drivers/mmc/core/sdio_io.c — go read the source, it's giving open book exam. 📖

like yes that's a lot of besties but they're all in the same friend group, iykyk. 🌈

mwah 💋 this page lives in ./drivers/mmc/core and it's dated October 2026 — that's the source, the version, and the whole entire footer, periodt. go read your 16 bits responsibly. 🍓💜

📦 where this page comes from