r600_mmio_hdp_flush(9)

💖 r600_mmio_hdp_flush — a Kernel API Manual moment (section 9, bestie) 💖

okay so we're in the Kernel API Manual, section 9, and today's main character is r600_mmio_hdp_flush — the lil function that flushes the Host Data Path cache via MMIO. honestly iconic behaviour.

---

✨ NAME ✨

r600_mmio_hdp_flush — flush the Host Data Path cache via MMIO 🎀

---

🦋 SYNOPSIS 🦋

void r600_mmio_hdp_flush (struct radeon_device *rdev );

no cap, that's the whole signature. one function, one pointer, zero drama 💅

---

🌸 ARGUMENTS 🌸

• rdev — the radeon device structure. that's it, that's the argument. she's the whole vibe check 🫶

---

🔥 DESCRIPTION 🔥

okay so here's the tea ☕ — some R6XX/R7XX chips just... don't seem to take into account HDP flushes that get performed through the ring buffer. like, they simply do not acknowledge it. rude, honestly 😭

and the consequence? corruption in rendering 💀 the visuals get messed up. not slay. the bug lives over at http://bugzilla.kernel.org/show_bug.cgi?id=15186 if you wanna go read the whole saga.

so to avoid all that mess, what do we do? we directly perform the HDP flush by writing the register through MMIO. skip the ring buffer, go straight to the source. main character energy, no middleman ✨

fr fr though — this is a workaround for a real hardware quirk. the rendering corruption is the actual problem being dodged here, so don't write it off as a vibe 🚨

---

🌈 SEE ALSO 🌈

• Kernel file ./drivers/gpu/drm/radeon/r600.c — the source, go read her 📖
• r600_get_allowed_info_register(9)
• r600_get_xclk(9)
• r600_vram_gtt_location(9)
• r600_gfx_is_lockup(9)
• r600_semaphore_ring_emit(9)
• r600_copy_cpdma(9)
• r600_get_gpu_clock_counter(9)

the whole bestie lineup, all in one place 💜

---

and that's the page, bestie 🫶 this lil gem lives in ./drivers/gpu/drm/radeon and it's dated October 2026 — so yes, she's from the future, and yes, she still cares about HDP flushes. periodt. 💅✨🎀