ddw_read_ext(9)

💅 ddw_read_ext(9) — your fave Kernel API Manual page, now with ✨vibes✨

okay so bestie, welcome to ddw_read_ext(9) — yes that's the manual name, yes it's a mouthful, no we're not changing it. this is the little kernel helper that goes and fetches you the value of an DDW extension. it's giving "small function, big plot" honestly 🎀

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🌸 NAME 🌸

ddw_read_ext — Get the value of an DDW extension.

like literally that's the whole job. iconic.

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✨ SYNOPSIS ✨

int ddw_read_ext (const struct device_node *np , int extnum , u32 *value
);

three arguments, one int coming back at you, no cap. 💅

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🦋 ARGUMENTS 🦋

• np — the device node from which the extension value is to be read. this is the friend you're asking for the tea. 🫶
• extnum — index number of the extension. basically which slot in the list you're peeking at, bestie. 🔍
• value — pointer to return value, modified when extension is available. so it doesn't just hold the value, it gets updated when that extension is actually there. 👑

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💖 DESCRIPTION 💖

so here's the lore: it checks if "ibm,ddw-extensions" exists for this node, and gets the value on index 'extnum'. that's it, that's the whole function, and honestly it ate. 🍓

and listen — the way it's also useful just for checking whether a property exists at all? you do that by passing value == NULL. literally a vibe check for properties, iykyk. ⭐

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🔥 RETURN 🔥

• 0 — if extension successfully read. slay, everything worked. 💚
• -EINVAL — returned if the "ibm,ddw-extensions" does not exist. it's not there, bestie. 💀
• -ENODATA — returned if "ibm,ddw-extensions" does not have a value. exists but empty, the worst kind of situation. 😭
• -EOVERFLOW — returned if "ibm,ddw-extensions" does not contain this extension. you asked for a slot that isn't in the list. 🙈

fr fr check these return codes, don't just assume it worked. that's the main character move here. 💅

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🌈 SEE ALSO 🌈

• Kernel file ./arch/powerpc/platforms/pseries/iommu.c — go read it, that's where the whole situation lives. 👑

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🧚 and that's the page!! brought to you by the fine folks over at ./arch/powerpc/platforms/pseries, dated October 2026, in the Kernel API Manual. mwah, go read some kernel source, ily, bye bestie 💜✨