sdio_writeb(9)

💅 sdio_writeb(9) — like, the Kernel API Manual, but make it make sense

okay so bestie, welcome to sdio_writeb(9) from the Kernel API Manual — yes it's a real kernel function and yes it's lowkey iconic. it writes one single byte to an SDIO function. one. byte. minimalism ate fr fr 💖

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✨ SYNOPSIS ✨

void sdio_writeb (struct sdio_func *func , u8 b , unsigned int addr ,
       int *err_ret );

look at her go. five-ish things in, nothing out, very mysterious main character energy 🎀

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🌸 ARGUMENTS 🌸

• func — the SDIO function you're accessing, i.e. the thing you're writing into. your little target 🫶
• b — the byte you want to write. it's a u8, so one byte, no more, no notes 💅
• addr — the address you're writing to. it's an unsigned int, so pick your spot wisely ✨
• err_ret — optional status value from the transfer. optional!! she's not mandatory, but she will tell you how it went 👀

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💜 DESCRIPTION 💜

So basically: this writes a single byte to the address space of a given SDIO function. that's it, that's the whole vibe. one byte, one address, no drama.

and err_ret will contain the status of the actual transfer — so if you passed in a pointer, you get the tea on whether it worked or not. ngl it's giving "small function, big responsibility" 🔥

reminder: err_ret is described as optional, so don't act surprised when it's a pointer you can skip. the status of the actual transfer is what lands there when you do pass it 🦋

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👑 SEE ALSO 👑

kernel file ./drivers/mmc/core/sdio_io.c — and literally the whole SDIO friend group, all here, all slaying:

• 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_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_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)

like, the whole group chat showed up. we love a supportive community 🌈

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okay that's the page!! this one came from ./drivers/mmc/core, dated October 2026, and it's filed under sdio_writeb(9) in the Kernel API Manual. go write your one byte bestie, you got this 💖✨🍓