Re: [PATCH] media: iris: optimize COMV buffer allocation for VPU3x and VPU4x

[Bryan O'Donoghue <bod@kernel.org>]

On 21/04/2026 07:41, Vishnu Reddy wrote:
> The existing iris_vpu_dec_comv_size() used VIDEO_MAX_FRAME (32) as
> num_comv count unconditionally when calculating the COMV buffer size.
> This resulted in an oversized COMV buffer allocation throughout decode
> session, wasting memory regardless of actual number of buffers required.

You should define what a COMV buffer is before talking about how you are 
changing it, i.e. define the term Co-located Motion Vector (CMOV) and 
then use the abbreviation CMOV liberally as you wish.

> For VPU3x and VPU4x platforms, introduce iris_vpu3x_4x_dec_comv_size() to
> replace iris_vpu_dec_comv_size(). It derives num_comv dynamically, it

"These derive num_cmove dynamically"

> uses inst->fw_min_count once the firmware has reported its minimum buffer
> requirements, and fallback to inst->buffers[BUF_OUTPUT].min_count during
> initialization before firmware has communicated its requirements. This
> aligns the COMV buffer size to the actual count needed rather than always
> allocating with fixed VIDEO_MAX_FRAME value.
> 
> Additionally, during iris_vdec_inst_init(), fw_min_count was initialized
> to MIN_BUFFERS instead of 0. This masked the fallback logic and caused the
> COMV size calculation to use MIN_BUFFERS even before firmware had reported
> its actual requirements. Fix this by initializing fw_min_count to 0.
> 
> During testing of 1080p AVC, it reduces the COMV buffer size from 32.89MB
> to 6.16MB per decode session, significantly reducing memory consumption.

Cool nice fix.

> 
> Signed-off-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
> ---
>   drivers/media/platform/qcom/iris/iris_vdec.c       |  2 +-
>   drivers/media/platform/qcom/iris/iris_vpu_buffer.c | 24 +++++++++++++++++++---
>   drivers/media/platform/qcom/iris/iris_vpu_buffer.h |  1 +
>   3 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/iris/iris_vdec.c b/drivers/media/platform/qcom/iris/iris_vdec.c
> index 719217399a30..f433065e08b2 100644
> --- a/drivers/media/platform/qcom/iris/iris_vdec.c
> +++ b/drivers/media/platform/qcom/iris/iris_vdec.c
> @@ -24,7 +24,7 @@ int iris_vdec_inst_init(struct iris_inst *inst)
>   	inst->fmt_src = kzalloc_obj(*inst->fmt_src);
>   	inst->fmt_dst = kzalloc_obj(*inst->fmt_dst);
> 
> -	inst->fw_min_count = MIN_BUFFERS;
> +	inst->fw_min_count = 0;
> 
>   	f = inst->fmt_src;
>   	f->type = V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE;
> diff --git a/drivers/media/platform/qcom/iris/iris_vpu_buffer.c b/drivers/media/platform/qcom/iris/iris_vpu_buffer.c
> index 9270422c1601..57237543b229 100644
> --- a/drivers/media/platform/qcom/iris/iris_vpu_buffer.c
> +++ b/drivers/media/platform/qcom/iris/iris_vpu_buffer.c
> @@ -731,6 +731,23 @@ static u32 iris_vpu_dec_comv_size(struct iris_inst *inst)
>   	u32 height = f->fmt.pix_mp.height;
>   	u32 width = f->fmt.pix_mp.width;
> 
> +	if (inst->codec == V4L2_PIX_FMT_H264)
> +		return hfi_buffer_comv_h264d(width, height, num_comv);
> +	else if (inst->codec == V4L2_PIX_FMT_HEVC)
> +		return hfi_buffer_comv_h265d(width, height, num_comv);
> +
> +	return 0;
> +}
> +
> +static u32 iris_vpu3x_4x_dec_comv_size(struct iris_inst *inst)
> +{
> +	struct v4l2_format *f = inst->fmt_src;
> +	u32 height = f->fmt.pix_mp.height;
> +	u32 width = f->fmt.pix_mp.width;
> +	u32 num_comv;
> +
> +	num_comv = inst->fw_min_count ? inst->fw_min_count : inst->buffers[BUF_OUTPUT].min_count;

Please just if/else this though its far easier to read/understand that way.

> +
>   	if (inst->codec == V4L2_PIX_FMT_H264)
>   		return hfi_buffer_comv_h264d(width, height, num_comv);
>   	else if (inst->codec == V4L2_PIX_FMT_HEVC)
> @@ -739,7 +756,8 @@ static u32 iris_vpu_dec_comv_size(struct iris_inst *inst)
>   		if (inst->fw_caps[DRAP].value)
>   			return 0;
>   		else
> -			return hfi_buffer_comv_av1d(width, height, num_comv);
> +			return hfi_buffer_comv_av1d(width, height,
> +						    num_comv + AV1D_COMV_BUFFER_OVERHEAD);
>   	}
> 
>   	return 0;
> @@ -2025,7 +2043,7 @@ u32 iris_vpu_buf_size(struct iris_inst *inst, enum iris_buffer_type buffer_type)
> 
>   	static const struct iris_vpu_buf_type_handle dec_internal_buf_type_handle[] = {
>   		{BUF_BIN,         iris_vpu_dec_bin_size             },
> -		{BUF_COMV,        iris_vpu_dec_comv_size            },
> +		{BUF_COMV,        iris_vpu3x_4x_dec_comv_size       },
>   		{BUF_NON_COMV,    iris_vpu_dec_non_comv_size        },
>   		{BUF_LINE,        iris_vpu_dec_line_size            },
>   		{BUF_PERSIST,     iris_vpu_dec_persist_size         },
> @@ -2098,7 +2116,7 @@ u32 iris_vpu4x_buf_size(struct iris_inst *inst, enum iris_buffer_type buffer_typ
> 
>   	static const struct iris_vpu_buf_type_handle dec_internal_buf_type_handle[] = {
>   		{BUF_BIN,         iris_vpu_dec_bin_size         },
> -		{BUF_COMV,        iris_vpu_dec_comv_size        },
> +		{BUF_COMV,        iris_vpu3x_4x_dec_comv_size   },
>   		{BUF_NON_COMV,    iris_vpu_dec_non_comv_size    },
>   		{BUF_LINE,        iris_vpu4x_dec_line_size      },
>   		{BUF_PERSIST,     iris_vpu4x_dec_persist_size   },
> diff --git a/drivers/media/platform/qcom/iris/iris_vpu_buffer.h b/drivers/media/platform/qcom/iris/iris_vpu_buffer.h
> index 12640eb5ed8c..7a9cc1c92da3 100644
> --- a/drivers/media/platform/qcom/iris/iris_vpu_buffer.h
> +++ b/drivers/media/platform/qcom/iris/iris_vpu_buffer.h
> @@ -110,6 +110,7 @@ struct iris_inst;
>   #define MAX_PE_NBR_DATA_LCU16_LINE_BUFFER_SIZE 96
>   #define AV1D_NUM_HW_PIC_BUF    16
>   #define AV1D_NUM_FRAME_HEADERS 16
> +#define AV1D_COMV_BUFFER_OVERHEAD 7

Whats this ? Why is there a new seven byte overhead ? Does it represent 
a header, an alignment ?

An overhead can mean anything.

>   #define SIZE_AV1D_SEQUENCE_HEADER 768
>   #define SIZE_AV1D_METADATA        512
>   #define SIZE_AV1D_FRAME_HEADER    1280
> 
> ---
> base-commit: 4fbeef21f5387234111b5d52924e77757626faa5
> change-id: 20260421-optimize_comv_buffer-ae7107673609
> 
> Best regards,
> --
> Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
>