drm/amdgpu/hdp4: use memcfg register to post the write for HDP flush

commit f690e3974755a650259a45d71456decc9c96a282 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: c9b8dcabb52a ("drm/amdgpu/hdp4.0: do a posting read when flushing HDP")
Reported-by: Alexey Klimov <alexey.klimov@linaro.org>
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 <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 5c937b4a6050316af37ef214825b6340b5e9e391)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/amd/amdgpu/hdp_v4_0.c b/drivers/gpu/drm/amd/amdgpu/hdp_v4_0.c
index 30210613dc5c47a65ae75a0988b050dcd87e19b4..2f3054ed7b1b5be090e0eaf8048d1c11d9ea9756 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/hdp_v4_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/hdp_v4_0.c
@@ -42,7 +42,12 @@ static void hdp_v4_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);
        }