drm/amdgpu/hdp7: use memcfg register to post the write for HDP flush

commit 5a11a27 upstream.

Reading back the remapped HDP flush register seems to cause
problems on some platforms. All we need is a read, so read back
the memcfg register.

Fixes: 6892751 ("drm/amdgpu/hdp7.0: do a posting read when flushing HDP")
Reported-by: Alexey Klimov <[email protected]>
Link: https://lists.freedesktop.org/archives/amd-gfx/2025-April/123150.html
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4119
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3908
Reviewed-by: Felix Kuehling <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
(cherry picked from commit dbc064a)
Cc: [email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: alexdeucher

drivers/gpu/drm/amd/amdgpu/hdp_v7_0.c

@@ -33,7 +33,12 @@ static void hdp_v7_0_flush_hdp(struct amdgpu_device *adev,
 {
 	if (!ring || !ring->funcs->emit_wreg) {
 		WREG32((adev->rmmio_remap.reg_offset + KFD_MMIO_REMAP_HDP_MEM_FLUSH_CNTL) >> 2, 0);
-		RREG32((adev->rmmio_remap.reg_offset + KFD_MMIO_REMAP_HDP_MEM_FLUSH_CNTL) >> 2);
+		/* We just need to read back a register to post the write.
+		 * Reading back the remapped register causes problems on
+		 * some platforms so just read back the memory size register.
+		 */
+		if (adev->nbio.funcs->get_memsize)
+			adev->nbio.funcs->get_memsize(adev);
 	} else {
 		amdgpu_ring_emit_wreg(ring, (adev->rmmio_remap.reg_offset + KFD_MMIO_REMAP_HDP_MEM_FLUSH_CNTL) >> 2, 0);
 	}