Re: [PATCH 2/2] media: iris: disable time-delta-based rate control for VBR
From: Vikash Garodia
Date: Tue Jul 07 2026 - 05:11:01 EST
On 7/7/2026 12:05 PM, Vishnu Reddy wrote:
From: Gourav Kumar <gouravk@xxxxxxxxxxxxxxxx>
The iris encoder driver was not sending
HFI_PROP_TIME_DELTA_BASED_RATE_CONTROL to the firmware during encoder
initialization. Without this property, the firmware defaults to
time-delta-based rate control (enabled), which calculates the output
bitrate from actual frame timing rather than following the configured
bitrate target.
This caused variable bitrate (VBR) encoding to produce ~5x configured
bitrate. For example, with video_bitrate=896000 (896 Kbps), the output
is ~4.4 Mbps instead of the expected ~896 Kbps.
Time-delta-based rate control is designed for variable frame rate (VFR)
scenarios where the encoder adapts to actual frame timing. However, when
an application explicitly configures a bitrate target, the firmware must
follow that target regardless of frame timing.
same here, we can drop the new empty lines
Fix this by adding the TIME_DELTA_BASED_RC capability with a default value
of 0 (disabled) and sending HFI_PROP_TIME_DELTA_BASED_RATE_CONTROL = 0 to
the firmware during stream-on, allowing the firmware to use the configured
bitrate as the target.
Signed-off-by: Gourav Kumar <gouravk@xxxxxxxxxxxxxxxx>
Signed-off-by: Vishnu Reddy <busanna.reddy@xxxxxxxxxxxxxxxx>
---
drivers/media/platform/qcom/iris/iris_ctrls.c | 19 +++++++++++++++++++
drivers/media/platform/qcom/iris/iris_ctrls.h | 1 +
drivers/media/platform/qcom/iris/iris_hfi_gen2.c | 10 ++++++++++
.../media/platform/qcom/iris/iris_hfi_gen2_defines.h | 1 +
.../media/platform/qcom/iris/iris_platform_common.h | 1 +
5 files changed, 32 insertions(+)
diff --git a/drivers/media/platform/qcom/iris/iris_ctrls.c b/drivers/media/platform/qcom/iris/iris_ctrls.c
index 10e33b8a73f6..f6136e655b98 100644
--- a/drivers/media/platform/qcom/iris/iris_ctrls.c
+++ b/drivers/media/platform/qcom/iris/iris_ctrls.c
@@ -1477,6 +1477,25 @@ int iris_set_layer_bitrate(struct iris_inst *inst, enum platform_inst_fw_cap_typ
&bitrate, sizeof(u32));
}
+int iris_set_time_delta_based_rc(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id)
+{
+ const struct iris_hfi_session_ops *hfi_ops = inst->hfi_session_ops;
+ u32 hfi_id = inst->fw_caps[cap_id].hfi_id;
+ u32 value = inst->fw_caps[cap_id].value;
+
+ /*
+ * Disable time-delta-based rate control (value = 0).
+ * This overrides the firmware's default (enabled), ensuring the
+ * firmware uses the configured bitrate target rather than calculating
+ * bitrate from frame timing.
+ */
+ return hfi_ops->session_set_property(inst, hfi_id,
+ HFI_HOST_FLAGS_NONE,
+ iris_get_port_info(inst, cap_id),
+ HFI_PAYLOAD_U32,
+ &value, sizeof(u32));
+}
+
int iris_set_properties(struct iris_inst *inst, u32 plane)
{
const struct iris_hfi_session_ops *hfi_ops = inst->hfi_session_ops;
diff --git a/drivers/media/platform/qcom/iris/iris_ctrls.h b/drivers/media/platform/qcom/iris/iris_ctrls.h
index 3c462ec9190b..10e046722ad3 100644
--- a/drivers/media/platform/qcom/iris/iris_ctrls.h
+++ b/drivers/media/platform/qcom/iris/iris_ctrls.h
@@ -47,6 +47,7 @@ int iris_set_layer_type(struct iris_inst *inst, enum platform_inst_fw_cap_type c
int iris_set_layer_count_gen1(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id);
int iris_set_layer_count_gen2(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id);
int iris_set_layer_bitrate(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id);
+int iris_set_time_delta_based_rc(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id);
int iris_set_properties(struct iris_inst *inst, u32 plane);
#endif
diff --git a/drivers/media/platform/qcom/iris/iris_hfi_gen2.c b/drivers/media/platform/qcom/iris/iris_hfi_gen2.c
index acc0ed8adda1..d119ad599c31 100644
--- a/drivers/media/platform/qcom/iris/iris_hfi_gen2.c
+++ b/drivers/media/platform/qcom/iris/iris_hfi_gen2.c
@@ -416,6 +416,16 @@ static const struct platform_inst_fw_cap inst_fw_cap_sm8550_enc[] = {
targets other than the one using inst_fw_cap_sm8550_enc ?
.flags = CAP_FLAG_OUTPUT_PORT | CAP_FLAG_MENU,
.set = iris_set_bitrate_mode_gen2,
},
+ {
+ .cap_id = TIME_DELTA_BASED_RC,
+ .min = 0,
+ .max = 1,
+ .step_or_mask = 1,
+ .value = 0,
+ .hfi_id = HFI_PROP_TIME_DELTA_BASED_RATE_CONTROL,
+ .flags = CAP_FLAG_OUTPUT_PORT,
+ .set = iris_set_time_delta_based_rc,
+ },
{
.cap_id = FRAME_SKIP_MODE,
.min = V4L2_MPEG_VIDEO_FRAME_SKIP_MODE_DISABLED,
diff --git a/drivers/media/platform/qcom/iris/iris_hfi_gen2_defines.h b/drivers/media/platform/qcom/iris/iris_hfi_gen2_defines.h
index 776b21cd11b2..8766d9e49611 100644
--- a/drivers/media/platform/qcom/iris/iris_hfi_gen2_defines.h
+++ b/drivers/media/platform/qcom/iris/iris_hfi_gen2_defines.h
@@ -67,6 +67,7 @@ enum hfi_rate_control {
};
#define HFI_PROP_RATE_CONTROL 0x0300012a
+#define HFI_PROP_TIME_DELTA_BASED_RATE_CONTROL 0x0300012b
#define HFI_PROP_QP_PACKED 0x0300012e
#define HFI_PROP_MIN_QP_PACKED 0x0300012f
#define HFI_PROP_MAX_QP_PACKED 0x03000130
diff --git a/drivers/media/platform/qcom/iris/iris_platform_common.h b/drivers/media/platform/qcom/iris/iris_platform_common.h
index c9256f2323dc..99dc6d5c72ba 100644
--- a/drivers/media/platform/qcom/iris/iris_platform_common.h
+++ b/drivers/media/platform/qcom/iris/iris_platform_common.h
@@ -183,6 +183,7 @@ enum platform_inst_fw_cap_type {
LAYER3_BITRATE_HEVC,
LAYER4_BITRATE_HEVC,
LAYER5_BITRATE_HEVC,
+ TIME_DELTA_BASED_RC,
INST_FW_CAP_MAX,
};
Regards,
Vikash