linux-kernel - Re: [PATCH 2/3] drm:msm: Initial Add Writeback Support

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Message-ID: <1427967609.10518.33.camel@x220>
Date:	Thu, 02 Apr 2015 11:40:09 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Jilai Wang <jilaiw@...eaurora.org>
Cc:	dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org, robdclark@...il.com
Subject: Re: [PATCH 2/3] drm:msm: Initial Add Writeback Support

A few nits follow.

On Wed, 2015-04-01 at 17:12 -0400, Jilai Wang wrote:
> --- a/drivers/gpu/drm/msm/Kconfig
> +++ b/drivers/gpu/drm/msm/Kconfig

> +config DRM_MSM_WB
> +	bool "Enable writeback support for MSM modesetting driver"
> +	depends on DRM_MSM
> +	depends on VIDEO_V4L2
> +	select VIDEOBUF2_CORE
> +	default y
> +	help
> +	  Choose this option if you have a need to support writeback
> +	  connector.

DRM_MSM_WB is a bool symbol...

> --- a/drivers/gpu/drm/msm/Makefile
> +++ b/drivers/gpu/drm/msm/Makefile
 
> +msm-$(CONFIG_DRM_MSM_WB) += \
> +	mdp/mdp5/mdp5_wb_encoder.o \
> +	mdp/mdp_wb/mdp_wb.o \
> +	mdp/mdp_wb/mdp_wb_connector.o \
> +	mdp/mdp_wb/mdp_wb_v4l2.o

so mdp_wb_v4l2.o will never be part of a module.

> --- /dev/null
> +++ b/drivers/gpu/drm/msm/mdp/mdp_wb/mdp_wb_v4l2.c

> +#include <linux/module.h>

This include is needed mostly for module_param(), right?

> +#define MSM_WB_MODULE_NAME "msm_wb"

MSM_WB_DRIVER_NAME? But see below.

> +static unsigned debug;
> +module_param(debug, uint, 0644);

debug is basically a boolean type of flag. Would
    static bool debug;
    module_param(debug, bool, 0644);

work?

> +MODULE_PARM_DESC(debug, "activates debug info");

No one is ever going to see this description.

> +#define dprintk(dev, level, fmt, arg...) \
> +	v4l2_dbg(level, debug, &dev->v4l2_dev, fmt, ## arg)

All instances of dprintk() that I found had level set to 1, so the above
could be simplified a bit:
    #define dprintk(dev, fmt, arg...) \
    	v4l2_dbg(1, debug, &dev->v4l2_dev, fmt, ## arg)

But perhaps pr_debug() and the dynamic debug facility could be used
instead of module_param(), dprintk() and v4l2_dbg(). Not sure which
approach is easier.

> +static const struct v4l2_file_operations msm_wb_v4l2_fops = {
> +	.owner = THIS_MODULE,

THIS_MODULE will basically be equivalent to NULL.

> +	.open = v4l2_fh_open,
> +	.release = vb2_fop_release,
> +	.poll = vb2_fop_poll,
> +	.unlocked_ioctl = video_ioctl2,
> +};

> +int msm_wb_v4l2_init(struct msm_wb *wb)
> +{
> +	struct msm_wb_v4l2_dev *dev;
> +	struct video_device *vfd;
> +	struct vb2_queue *q;
> +	int ret;
> +
> +	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +	if (!dev)
> +		return -ENOMEM;
> +
> +	snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
> +			"%s", MSM_WB_MODULE_NAME);

It looks like you can actually drop the #define and merge the last two
arguments to snprintf() into just "msm_wb".

> +	ret = v4l2_device_register(NULL, &dev->v4l2_dev);
> +	if (ret)
> +		goto free_dev;
> +
> +	/* default ARGB8888 640x480 */
> +	dev->fmt = get_format(V4L2_PIX_FMT_RGB32);
> +	dev->width = 640;
> +	dev->height = 480;
> +
> +	/* initialize queue */
> +	q = &dev->vb_vidq;
> +	q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
> +	q->io_modes = VB2_DMABUF;
> +	q->drv_priv = dev;
> +	q->buf_struct_size = sizeof(struct msm_wb_v4l2_buffer);
> +	q->ops = &msm_wb_vb2_ops;
> +	q->mem_ops = &msm_wb_vb2_mem_ops;
> +	q->timestamp_type = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> +
> +	ret = vb2_queue_init(q);
> +	if (ret)
> +		goto unreg_dev;
> +
> +	mutex_init(&dev->mutex);
> +
> +	vfd = &dev->vdev;
> +	*vfd = msm_wb_v4l2_template;
> +	vfd->debug = debug;

I couldn't find a member of struct video_device named debug. Where does
that come from? Because, as far as I can see, this won't compile.

> +	vfd->v4l2_dev = &dev->v4l2_dev;
> +	vfd->queue = q;
> +
> +	/*
> +	 * Provide a mutex to v4l2 core. It will be used to protect
> +	 * all fops and v4l2 ioctls.
> +	 */
> +	vfd->lock = &dev->mutex;
> +	video_set_drvdata(vfd, dev);
> +
> +	ret = video_register_device(vfd, VFL_TYPE_GRABBER, -1);
> +	if (ret < 0)
> +		goto unreg_dev;
> +
> +	dev->wb = wb;
> +	wb->wb_v4l2 = dev;
> +	v4l2_info(&dev->v4l2_dev, "V4L2 device registered as %s\n",
> +		  video_device_node_name(vfd));
> +
> +	return 0;
> +
> +unreg_dev:
> +	v4l2_device_unregister(&dev->v4l2_dev);
> +free_dev:
> +	kfree(dev);
> +	return ret;
> +}


Paul Bolle

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