Re: [PATCH v4 3/6] media: iris: add iris4 specific H265 line buffer calculation

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] media: iris: quadratic scaling of dpb_obp due to double multiplication
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commit 8ebbe0addefc2c9da9b09f0ae52a879bbb0ec3f3
Author: Vikash Garodia <vikash.garodia@oss.qualcomm.com>

media: iris: add iris4 specific H265 line buffer calculation

This commit introduces a new H265 decoder line buffer size calculation
formula for iris4 (VPU4). It resolves firmware failures seen with specific
test vectors by providing a larger buffer size for certain configurations.

> diff --git a/drivers/media/platform/qcom/iris/iris_vpu_buffer.c b/drivers/media/platform/qcom/iris/iris_vpu_buffer.c
> index faebb54728660..a99b8030e3dd0 100644
> --- a/drivers/media/platform/qcom/iris/iris_vpu_buffer.c
> +++ b/drivers/media/platform/qcom/iris/iris_vpu_buffer.c
[ ... ]
> @@ -1814,6 +1814,63 @@ static u32 hfi_vpu4x_buffer_line_vp9d(u32 frame_width, u32 frame_height, u32 _yu
[ ... ]
> +static u32 hfi_vpu4x_buffer_line_h265d(u32 frame_width, u32 frame_height, bool is_opb,
> +				       u32 num_vpp_pipes)
> +{
[ ... ]
> +	if (is_opb)
> +		dpb_obp = size_dpb_opb(frame_height, lcu_size) * num_vpp_pipes;
> +
[ ... ]
> +	return ((ALIGN(dpb_obp, DMA_ALIGNMENT) + ALIGN(se_left_lb, DMA_ALIGNMENT) +
> +		ALIGN(vsp_left_lb, DMA_ALIGNMENT)) * num_vpp_pipes) +

[Severity: Medium]
Does this code multiply dpb_obp by num_vpp_pipes twice?

Earlier in this function, dpb_obp is calculated with a multiplication by
num_vpp_pipes. Then it is included in the return statement here, where the
sum containing dpb_obp is multiplied by num_vpp_pipes again. 

This results in quadratic scaling for the dpb_obp portion of the buffer
size. Is this double multiplication intentional, or should one of the
multipliers be removed to prevent over-allocating the line buffer?

> +		ALIGN(fe_left_lb, DMA_ALIGNMENT) + ALIGN(top_lb, DMA_ALIGNMENT) +
> +		ALIGN(qp_size, DMA_ALIGNMENT);
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20261001-kaanapali-iris-v4-0-642f9ac5e699@oss.qualcomm.com?part=3