Re: [PATCH v6 3/4] media: raspberrypi: Add support for RP1-CFE

Hans Verkuil
2024-10-24T08:22:14Z

Hi Tomi,

I know this driver is already merged, but while checking for drivers that use
q->max_num_buffers I stumbled on this cfe code:

<snip>

> +/*
> + * vb2 ops
> + */
> +
> +static int cfe_queue_setup(struct vb2_queue *vq, unsigned int *nbuffers,
> + unsigned int *nplanes, unsigned int sizes[],
> + struct device *alloc_devs[])
> +{
> + struct cfe_node *node = vb2_get_drv_priv(vq);
> + struct cfe_device *cfe = node->cfe;
> + unsigned int size = is_image_node(node) ?
> + node->vid_fmt.fmt.pix.sizeimage :
> + node->meta_fmt.fmt.meta.buffersize;
> +
> + cfe_dbg(cfe, "%s: [%s] type:%u\n", __func__, node_desc[node->id].name,
> + node->buffer_queue.type);
> +
> + if (vq->max_num_buffers + *nbuffers < 3)
> + *nbuffers = 3 - vq->max_num_buffers;

This makes no sense: max_num_buffers is 32, unless explicitly set when vb2_queue_init
is called. So 32 + *nbuffers is never < 3.

If the idea is that at least 3 buffers should be allocated by REQBUFS, then set
q->min_reqbufs_allocation = 3; before calling vb2_queue_init and vb2 will handle this
for you.

Drivers shouldn't modify *nbuffers, except in very rare circumstances, especially
since the code is almost always wrong.

Regards,

Hans

> +
> + if (*nplanes) {
> + if (sizes[0] < size) {
> + cfe_err(cfe, "sizes[0] %i < size %u\n", sizes[0], size);
> + return -EINVAL;
> + }
> + size = sizes[0];
> + }
> +
> + *nplanes = 1;
> + sizes[0] = size;
> +
> + return 0;
> +}