sdio_writeb_readb(9)

💅 sdio_writeb_readb(9) — the Kernel API Manual, bestie edition 🎀

okay so real talk — you're in the Kernel API Manual, and the page you want is sdio_writeb_readb. that's the one. no cap, this is the whole vibe: write a byte, read it right back, all in one little request. ✨

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🌸 NAME 🌸

sdio_writeb_readb — write and read a byte from SDIO function 🦋

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✨ SYNOPSIS ✨

u8 sdio_writeb_readb (struct sdio_func *func , u8 write_byte , unsigned
int addr , int *err_ret );

like, that's the whole signature. iconic. keep it verbatim or it's not gonna compile, and we do NOT want that energy 😭

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🎀 ARGUMENTS 🎀

• func — the SDIO function you're accessing 💖 that's your main character right there.
• write_byte — the byte you're writing. literally just the byte. one (1) byte.
• addr — the address you're writing to. 📍
• err_ret — optional status value from the transfer. it's optional, but honestly bestie, you're gonna want it.

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🫶 DESCRIPTION 🫶

so here's what's happening: this does a RAW (Read After Write) operation, exactly as defined by the SDIO spec 🔥

a single byte gets written to the address space of a given SDIO function, and then the response gets read back from that same address — and the way that it does both of those is with a single request. one shot. ate. 💅

now for the not-so-slay part: if there's a problem with the operation, 0xff is returned and err_ret will contain the error code 💀 so heads up, 0xff is your "something went wrong" flag, not a real read. don't get caught out by that, iykyk.

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👑 SEE ALSO 👑

the kernel file lives at ./drivers/mmc/core/sdio_io.c — go read it if you're feeling nerdy 🧚 and here's the whole friend group:

• 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_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_readb(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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that's the page, bestie 💜 this lil beauty comes to you from the Kernel API Manual, sourced out of ./drivers/mmc/core, and it's dated October 2026 — go forth and write-then-read responsibly, mwah 🎀✨