intel_wm_method2(9)

💅 intel_wm_method2 — Kernel API Manual, bestie edition ✨

okay so picture this: it's giving manual page, it's giving DRM/i915 display watermark math, and you're the main character who needs to know how much FIFO to hand over. The function is called intel_wm_method2, and it lives its little life in the Kernel API Manual. Let's get into it 🫶

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✨ NAME ✨

intel_wm_method2 — the Method 2 / "large buffer" watermark formula, no cap 🌸

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🦋 SYNOPSIS 🦋

unsigned int intel_wm_method2 (unsigned int pixel_rate , unsigned int
       htotal , unsigned int width , unsigned int cpp , unsigned int latency );

literally just five unsigned ints in and one unsigned int out, we love a clean signature 💖

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🎀 ARGUMENTS 🎀

• pixel_rate — the pipe pixel rate, measured in kHz ⭐
• htotal — the pipe horizontal total, iconic
• width — the plane width in pixels, yes bestie, pixels 🦋
• cpp — the plane's bytes per pixel, so like, how chunky each pixel is 💅
• latency — memory wakeup latency, and bestie listen, it's in 0.1us units so don't come at it with plain microseconds 🙈

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💜 DESCRIPTION 💜

So what are we even doing here? We're computing the watermark with the method 2 — aka the "large buffer" formula 🌈. And heads up: the caller is allowed to add extra cachelines on top of this to account for TLB misses and clock crossings. That's a you thing, not a this function thing, iykyk ✨

This method is obsessed (affectionate) with the long term drain rate of the FIFO — like, it does account for blanking periods, which effectively reduce the average drain rate across a longer period 👑. And the whole "large" thing? It's not about the buffer being large in a vague vibe sense — it refers to the fact that the FIFO is relatively large compared to the amount of data fetched. Periodt 💀

The FIFO level vs. time graph lowkey looks something like this:

|___       |___ |    ___   |    ___ |          |        __
--__--__--__--__--__--__ (- plane active, _ blanking) -> time

(that's - for plane active, _ for blanking, and the arrow means time, bestie 🕰️)

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🔥 RETURN 🔥

The watermark, in bytes. That's it, that's the tea 💖

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🌸 SEE ALSO 🌸

• Kernel file ./drivers/gpu/drm/i915/display/i9xx_wm.c 👑
• intel_set_memory_cxsr(9)
• intel_wm_method1(9)
• intel_calculate_wm(9)

go read those too, they're all in the same friend group fr fr 🫶

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and that's the whole page!! 💅 this lil icon comes to you from ./drivers/gpu/drm/i915/display, dated October 2026, and honestly? she ate. mwah 🍓✨