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

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

On Fri, Sep 22, 2023 at 01:16:21PM +0300, Tomi Valkeinen wrote:
> On 22/09/2023 13:09, Sakari Ailus wrote:
> > On Fri, Sep 22, 2023 at 12:53:20PM +0300, Laurent Pinchart wrote:
> >> On Fri, Sep 22, 2023 at 09:41:01AM +0000, Sakari Ailus wrote:
> >>> On Tue, Sep 19, 2023 at 06:21:23PM +0300, Laurent Pinchart wrote:
> >>>> On Tue, Sep 19, 2023 at 02:49:29PM +0000, Sakari Ailus wrote:
> >>>>> On Tue, Sep 19, 2023 at 04:32:48PM +0300, Laurent Pinchart wrote:
> >>>>>> 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
> >>>
> >>> I can count only 17 --- there's no newline.
> >>>
> >>> I guess it's most probably either of these then. X-)
> >>>
> >>>> 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.
> >>>
> >>> I can add a WARN_ON() to cover this.
> >>>
> >>>>>>> +
> >>>>>>> +		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 ?
> >>>
> >>> It works with data that would span more than 9 characters when printed.
> >>
> >> And 0x%02x doesn't ?
> > 
> > Ah, it should indeed work, 0 is actually a flag here and part of the field
> > width or precision. I can use that in v4.
> 
> Or %#04x, even shorter!

That's different though.

printf("0x%2.2x\n", 0);		-> 0x00
printf("0x%2.2x\n", 1);		-> 0x01
printf("0x%2.2x\n", 42);	-> 0x2a

printf("0x%02x\n", 0);		-> 0x00
printf("0x%02x\n", 1);		-> 0x01
printf("0x%02x\n", 42);		-> 0x2a

printf("%#2.2x\n", 0);		-> 00
printf("%#2.2x\n", 1);		-> 0x01
printf("%#2.2x\n", 42);		-> 0x2a

printf("%#02x\n", 0);		-> 00
printf("%#02x\n", 1);		-> 0x1
printf("%#02x\n", 42);		-> 0x2a

-- 
Regards,

Laurent Pinchart