sdio_readl(9)

🦋 sdio_readl — a Kernel API Manual page, bestie edition

okay so we're in the Kernel API Manual today and the star of the show is sdio_readl(9). she reads 32-bit integers out of an SDIO function and she does it flawlessly. come on. 💅

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🌸 NAME

sdio_readl — read a 32 bit integer from a SDIO function

like, literally. that's the whole job. 32 bits. one integer. iconic behavior. ✨

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✨ SYNOPSIS

u32 sdio_readl (struct sdio_func *func , unsigned int addr , int
*err_ret );

yes the formatting is a little crunchy, no we're not fixing it, it's called ✨character✨ 🎀

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💖 ARGUMENTS

• func — the SDIO function you're gonna access. your main character. 👑
• addr — the address you're reading from. like, where the tea is at. 📍
• err_ret — an optional status value from the transfer. so if things go sideways you actually find out instead of just vibing in the dark. 🙈

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🫶 DESCRIPTION

Reads a 32 bit integer from the address space of a given SDIO function. that's it, that's the plot. 🍓

but listen — there's a catch and you need to hear it:

If there is a problem reading the address, 0xffffffff is returned and err_ret will contain the error code. 💀

so like, if you see 0xffffffff come back, that is not a cute little integer that happens to be big. that is the "something went wrong" signal, bestie. check err_ret fr fr. don't be out here using 0xffffffff like it's real data, i'm begging. 😭

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🔥 SEE ALSO

the whole friend group, no cap. also shoutout to the kernel file ./drivers/mmc/core/sdio_io.c — that's where the sauce lives, iykyk. 🧚

• 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_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 readb / readw / readl trio alone? ate. 🔥

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🌈 the sign-off

this lil masterpiece comes to you from ./drivers/mmc/core, dated October 2026, and it goes out to every kernel dev who's ever squinted at a hex value at 2am. you're doing amazing sweetie. 💜🎀🦋

periodt. 💅