Re: [PATCH v2 30/36] media: imx: Fix misuse of min_buffers_needed field

[Philipp Zabel]

Hi Benjamin,

On Mo, 2023-12-04 at 14:23 +0100, Benjamin Gaignard wrote:
> 'min_buffers_needed' is suppose to be used to indicate the number
> of buffers needed by DMA engine to start streaming.
> imx-media-capture driver doesn't use DMA engine and just want to specify
> the minimum number of buffers to allocate when calling VIDIOC_REQBUFS.

This is used by imx-media-csi and imx-ic-prpencvf. Both expect two
buffers to setup the IDMAC DMA engine double buffer (see
csi_idmac_setup_vb2_buf()/prp_setup_vb2_buf()).

These functions can cope with less than two buffers queued, by using a
special "underrun" buffer as a workaround, but the hardware does
require two buffer addresses, so I'm not sure whether this really
should be called a misuse of min_buffers_needed.

regards
Philipp