On 12/15/2023 10:01, Hamza Mahfooz wrote:
There have recently been changes that break backwards compatibility,
that were introduced into DMUB firmware (for DCN32x) concerning FPO and
SubVP. So, since those are just power optimization features, we can just
disable them unless the user is using a new enough version of DMUB
firmware.

Cc: sta...@vger.kernel.org
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2870
Fixes: ed6e2782e974 ("drm/amd/display: For cursor P-State allow for SubVP")
Reported-by: Mikhail Gavrilov <mikhail.v.gavri...@gmail.com>
Closes: 
https://lore.kernel.org/r/cabxgcsnrb0qbf2pkljmdhvokxygd6-e+8p-4qo6fowa6zp2...@mail.gmail.com/
Signed-off-by: Hamza Mahfooz <hamza.mahf...@amd.com>

Reviewed-by: Mario Limonciello <mario.limoncie...@amd.com>

---
  drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c 
b/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
index 5c323718ec90..0f0972ad441a 100644
--- a/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
+++ b/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
@@ -960,6 +960,12 @@ void dcn32_init_hw(struct dc *dc)
                dc->caps.dmub_caps.subvp_psr = 
dc->ctx->dmub_srv->dmub->feature_caps.subvp_psr_support;
                dc->caps.dmub_caps.gecc_enable = 
dc->ctx->dmub_srv->dmub->feature_caps.gecc_enable;
                dc->caps.dmub_caps.mclk_sw = 
dc->ctx->dmub_srv->dmub->feature_caps.fw_assisted_mclk_switch;
+
+               if (dc->ctx->dmub_srv->dmub->fw_version <
+                   DMUB_FW_VERSION(7, 0, 35)) {
+                       dc->debug.force_disable_subvp = true;
+                       dc->debug.disable_fpo_optimizations = true;
+               }

One potential improvement would be to emit a message in this case to let the user know that this has happened and if they upgrade their firmware they can get additional power optimizations.

        }
  }

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