Re: [PATCH v3 2/4] media: qcom: camss: vfe-4-1: program the RDI write master buffer size

[Bryan O'Donoghue]

On 11/11/2026 13:53, Allan Siriani wrote:
> The RDI outputs use the write masters in frame based mode. In that mode
> vfe_wm_frame_based() only sets the FRM_BASED bit of WR_CFG and leaves
> WR_BUFFER_CFG and WR_IMAGE_SIZE untouched: they keep their reset value or
> whatever a previous line based (PIX) stream left there, so nothing tells
> the write master how big the buffer is. If the sensor sends more data
> than the configured format, the write master keeps writing past the end
> of the V4L2 buffer. When the CAMSS runs without an IOMMU, as on
> MSM8226 today (the SoC has one, but it is not described in the upstream
> DT; its VFE 4.0 shares this register layout), that corrupts unrelated
> memory.

This is a long and rambling problem description that looks like LLMese 
to me.

I would appreciate a more direct and succinct problem description.

"MSM8226 doesn't have an IOMMU defined. If a sensor writes more data 
than WR_BUFER_CFG and/or WR_IMW_SIZE expect we will get an overrun."

"Program WM_IMAGE_SIZE and WR_BUFFER_CFG to restrict the maximum size 
the write masters can write"
> Program WR_BUFFER_CFG in frame based mode as the downstream VFE 4.0/4.1
> driver does (msm_vfe40_axi_cfg_wm_reg(): words per line, lines minus one
> and burst length, IMAGE_SIZE unused), from the bytesperline and height
> of the active format, and clear it again when the write master is
> released.
>
> Pass the active format to the wm_frame_based() op for that. The VFE 4.7
> and 4.8 implementations, which use a different register layout, are left
> unchanged.
>
> Fixes: 4c98a5f57f90 ("media: camss: Add VFE files")
> Signed-off-by: Allan Siriani<allan@xxxxxxxxxxxxxxxxxxx>
> ---

Something like that. Please don't let the LLM write it for you - the 
word-salad is difficult to take in.

Commit logs should be elucidative not occluding in nature.

---
bod