sdio_f0_readb(9)

💖 sdio_f0_readb(9) — like, the Kernel API Manual entry, bestie 💖

okay so picture this: it's giving "one tiny byte, zero drama" and honestly? iconic. this is sdio_f0_readb from the kernel API manual, and she's here to grab exactly one (1) byte out of SDIO function 0's address space. no more, no less. main character energy fr fr 🎀

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✨ NAME ✨

sdio_f0_readb — read a single byte from SDIO function 0 🌸

✨ SYNOPSIS ✨

unsigned char sdio_f0_readb (struct sdio_func *func , unsigned int addr
, int *err_ret );

✨ ARGUMENTS ✨

• func — an SDIO function of the card 🦋 like, the function you're poking at
• addr — address to read 📍 the exact spot you want the byte from
• err_ret — optional status value from transfer 👀 optional in the sense that you can pass it, and if you do, it'll tell you how things went

✨ DESCRIPTION ✨

Reads a single byte from the address space of SDIO function 0. one byte. that's the whole vibe. 💅

If there is a problem reading the address, 0xff is returned and err_ret will contain the error code. so yeah — the failure signal is 0xff, and ngl that's exactly why you want to hand in an err_ret so you can actually tell "real byte" from "something went sideways" 😭 no cap, check it.

fr fr: 0xff on its own does not mean "the byte was 0xff." it means "bestie, there was an error." that's why err_ret exists 🫶

✨ SEE ALSO ✨

Kernel file ./drivers/mmc/core/sdio_io.c — and like, the whole girlies here, go say hi 👑

• sdio_claim_host(9)
• sdio_release_host(9)
• sdio_enable_func(9)
• sdio_disable_func(9)
• sdio_set_block_size(9)
• sdio_align_size(9)
• sdio_readb(9)
• sdio_writeb(9)
• sdio_writeb_readb(9)
• sdio_memcpy_fromio(9)
• sdio_memcpy_toio(9)
• sdio_readsb(9)
• sdio_writesb(9)
• sdio_readw(9)
• sdio_writew(9)
• sdio_readl(9)
• sdio_writel(9)
• sdio_f0_writeb(9)
• sdio_get_host_pm_caps(9)
• sdio_set_host_pm_flags(9)
• sdio_retune_crc_disable(9)
• sdio_retune_crc_enable(9)
• sdio_retune_hold_now(9)
• sdio_retune_release(9)

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k that's the whole page bestie, go read your one byte and slay 💜

🌷 mwah, this lil page lives in ./drivers/mmc/core, dated October 2026, and that's the sign-off 💫 bye pookie! 🍓