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

[Paul Bolle <pebolle@tiscali.nl>]

Hi Jilai,

On Thu, 2015-04-02 at 17:58 +0000, jilaiw@codeaurora.org wrote:
> Thanks Paul. Some comments embedded and for the rest I will update the
> code accordingly.

Most of my comments appear to be ill informed, so I wouldn't mind if
you'd specify which updates you actually plan to do.

> >> --- a/drivers/gpu/drm/msm/Makefile
> >> +++ b/drivers/gpu/drm/msm/Makefile
> >
> >> +msm-$(CONFIG_DRM_MSM_WB) += \
> >> +	mdp/mdp5/mdp5_wb_encoder.o \
> >> +	mdp/mdp_wb/mdp_wb.o \
> >> +	mdp/mdp_wb/mdp_wb_connector.o \
> >> +	mdp/mdp_wb/mdp_wb_v4l2.o
> >
> > so mdp_wb_v4l2.o will never be part of a module.
> If CONFIG-DRM_MSM_WB is y, then all wb related files (including
> mdp_wb_v4l2.o) will be added to msm-y, then be linked to msm.o
> obj-$(CONFIG_DRM_MSM)   += msm.o

(A tell tale was that I didn't quote that line.)

> Refer to document http://lwn.net/Articles/21835/ (section 3.3),
> it should be able to be built-in to kernel or as a module.

It's hard typing with a brown paper bag for headware: I still have
trouble speaking Makefile, even after all these years, but I'm afraid
you're right.

> >> --- /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.
> yes, it's there:
> http://lxr.free-electrons.com/source/include/media/v4l2-dev.h#L127

Probably in some tree I'm not aware of. I only did:
    $ git cat-file blob v4.0-rc6:include/media/v4l2-dev.h | grep debug
	/* Internal device debug flags, not for use by drivers */
	int dev_debug;

and
    $ git cat-file blob next-20150402:include/media/v4l2-dev.h | grep debug
	/* Internal device debug flags, not for use by drivers */
	int dev_debug;

Which tree does debug come from?

Thanks,


Paul Bolle