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

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Message-ID: <4d9e340e-2ae7-495b-8623-0d10398e1c3d@xs4all.nl>
Date: Thu, 24 Oct 2024 10:20:12 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Florian Fainelli <florian.fainelli@...adcom.com>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, Naushir Patuck
 <naush@...pberrypi.com>, Laurent Pinchart
 <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Jacopo Mondi <jacopo.mondi@...asonboard.com>,
 Kieran Bingham <kieran.bingham@...asonboard.com>
Subject: Re: [PATCH v6 3/4] media: raspberrypi: Add support for RP1-CFE

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;
> +}