Re: [PATCH v3 11/12] media: v4l: subdev: Print debug information on frame descriptor

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Tue, Sep 19, 2023 at 02:49:29PM +0000, Sakari Ailus wrote:
> Hi Laurent,
> 
> On Tue, Sep 19, 2023 at 04:32:48PM +0300, Laurent Pinchart wrote:
> > Hi Sakari,
> > 
> > Thank you for the patch.
> > 
> > On Tue, Sep 19, 2023 at 03:17:27PM +0300, Sakari Ailus wrote:
> > > Print debug level information on returned frame descriptors.
> > > 
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > ---
> > >  drivers/media/v4l2-core/v4l2-subdev.c | 32 ++++++++++++++++++++++++++-
> > >  1 file changed, 31 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > > index 7b087be3ff4f..504ca625b2bd 100644
> > > --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > > +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > > @@ -15,6 +15,7 @@
> > >  #include <linux/module.h>
> > >  #include <linux/overflow.h>
> > >  #include <linux/slab.h>
> > > +#include <linux/string.h>
> > >  #include <linux/types.h>
> > >  #include <linux/version.h>
> > >  #include <linux/videodev2.h>
> > > @@ -309,9 +310,38 @@ static int call_set_selection(struct v4l2_subdev *sd,
> > >  static int call_get_frame_desc(struct v4l2_subdev *sd, unsigned int pad,
> > >  			       struct v4l2_mbus_frame_desc *fd)
> > >  {
> > > +	unsigned int i;
> > > +	int ret;
> > > +
> > >  	memset(fd, 0, sizeof(*fd));
> > >  
> > > -	return sd->ops->pad->get_frame_desc(sd, pad, fd);
> > > +	ret = sd->ops->pad->get_frame_desc(sd, pad, fd);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	dev_dbg(sd->dev, "Frame descriptor on pad %u, type %s\n", pad,
> > > +		fd->type == V4L2_MBUS_FRAME_DESC_TYPE_PARALLEL ? "parallel" :
> > > +		fd->type == V4L2_MBUS_FRAME_DESC_TYPE_CSI2 ? "CSI-2" :
> > > +		"unknown");
> > > +
> > > +	for (i = 0; i < fd->num_entries; i++) {
> > > +		struct v4l2_mbus_frame_desc_entry *entry = &fd->entry[i];
> > > +		char buf[20] = "";
> > 
> > Should this be sized for the worst case ? The vc and dt should not be
> > large, but a buffer overflow on the stack in debug code if a subdev
> > returns an incorrect value would be bad.
> 
> 17 should be enough but it's not useful to use a size not divisible by 4 in
> practice here.

18 with the terminating 0. But indeed, it's large enough as vc and dt
are u8. I'm just a bit worried we're opening the door to hard to debug
problems if we later change the vc and dt types.

> > > +
> > > +		if (fd->type == V4L2_MBUS_FRAME_DESC_TYPE_CSI2)
> > > +			snprintf(buf, sizeof(buf), ", vc %u, dt 0x%2.2x",
> > 
> > 0x%02x would be one character shorter ;-) Same below.
> 
> It would be, but I prefer the above notation as it's more generic.

Out of curiosity, how so ?

> > > +				 entry->bus.csi2.vc, entry->bus.csi2.dt);
> > > +
> > > +		dev_dbg(sd->dev,
> > > +			"\tstream %u, code 0x%4.4x, lenght %u, flags%s%s%s\n",
> > 
> > s/lenght/length/
> 
> Thanks, I'll fix this.
> 
> > > +			entry->stream, entry->pixelcode, entry->length,
> > > +			entry->flags & V4L2_MBUS_FRAME_DESC_FL_LEN_MAX ?
> > > +			" LEN_MAX" : "",
> > > +			entry->flags & V4L2_MBUS_FRAME_DESC_FL_BLOB ?
> > > +			" BLOB" : "", buf);
> > 
> > If no flags are set, you will get something like
> > 
> > 	stream 0, code 0x1234, length ..., flags, vc 0, dt 0x2a
> > 
> > Maybe printing the hex value for the flags would be simpler and clearer
> > ?
> 
> How about adding the numerical value in addition to the strings?
> 
> The use of these flags is rare though. I could just remove the strings,
> too.

Up to you.

-- 
Regards,

Laurent Pinchart