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Message-ID: <20241213093413.GB19755@pendragon.ideasonboard.com>
Date: Fri, 13 Dec 2024 11:34:13 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Cosmin Tanislav <demonsingur@...il.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Hans Verkuil <hverkuil@...all.nl>,
Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
Paweł Anikiel <panikiel@...gle.com>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: v4l: subdev: Use dev_err() to print errors and
clarify
On Fri, Dec 13, 2024 at 08:33:09AM +0000, Sakari Ailus wrote:
> On Wed, Nov 27, 2024 at 09:20:33AM +0200, Laurent Pinchart wrote:
> > On Mon, Nov 25, 2024 at 10:34:40PM +0200, Cosmin Tanislav wrote:
> > > On 11/23/24 11:32 PM, Laurent Pinchart wrote:
> > > > On Fri, Nov 22, 2024 at 05:33:39PM +0200, Cosmin Tanislav wrote:
> > > >> The error values end up being returned to userspace, it makes sense to
> > > >> have some useful information printed when debugging them, even if the
> > > >> reason for the errors are bad configs or internal driver issues.
> > > >>
> > > >> Replace dev_dbg() with dev_err() for errors.
> > > >
> > > > We use dev_dbg() on purpose for all errors that can be triggered
> > > > directly by applications. This includes in particular all pipeline
> > > > validation errors.
> > > >
> > > > The error paths in this specific patch shouldn't be in that category, as
> > > > all the validation should have been performed before starting subdevs
> > > > (assuming all drivers are correctly implemented, which is of course not
> > > > a given, but those issues should be fixed). I think we could therefore
> > > > switch to dev_err() here. However, I'm wondering what kind of issues
> > > > triggered this patch. What errors did you run into that would have
> > > > benefited from being reported more loudly, and were they caused by
> > > > driver bugs or userspace misconfiguring the device ?
> > >
> > > I've had this patch in my GMSL2 tree for some time now, I believe indeed
> > > the reasons why I've hit these error cases were the drivers being
> > > slightly broken, but I still think it is worthwhile to show an error
> > > message, to aid with debugging. Adding the entity name to the messages
> > > makes it even more clear where exactly the code is breaking.
> > >
> > > I can split it up into separate patches for dev_dbg() -> dev_err() and
> > > adding the entity name to the print statements for V2.
> >
> > I'm OK either way. If other people prefer keeping dev_dbg() then
> > splitting the patch in two would make sense.
>
> dev_dbg() seems the correct function here: these are user-triggerable
> errors that aren't related to hardware conditions.
Are these user-triggerable in the absence of bugs in drivers ?
> > > >> Also, when using complex pipelines with multiple bridges between the
> > > >> video device and multiple source sub devices, printing just the video
> > > >> device name for each error does not provide enough context as to which
> > > >> operation failed.
> > > >>
> > > >> Add sub device entity name to the messages where possible to clarify the
> > > >> source of the errors.
> > > >
> > > > This can be considered as a standalone patch.
> > > >
> > > >> Signed-off-by: Cosmin Tanislav <demonsingur@...il.com>
> > > >> ---
> > > >> drivers/media/v4l2-core/v4l2-subdev.c | 22 ++++++++++++----------
> > > >> 1 file changed, 12 insertions(+), 10 deletions(-)
> > > >>
> > > >> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > > >> index 4f0eecd7fd66f..d51b4594d11c5 100644
> > > >> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > > >> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > > >> @@ -2303,20 +2303,21 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
> > > >> &found_streams, &enabled_streams);
> > > >>
> > > >> if (found_streams != streams_mask) {
> > > >> - dev_dbg(dev, "streams 0x%llx not found on %s:%u\n",
> > > >> + dev_err(dev, "streams 0x%llx not found on %s:%u\n",
> > > >> streams_mask & ~found_streams, sd->entity.name, pad);
> > > >> ret = -EINVAL;
> > > >> goto done;
> > > >> }
> > > >>
> > > >> if (enabled_streams) {
> > > >> - dev_dbg(dev, "streams 0x%llx already enabled on %s:%u\n",
> > > >> + dev_err(dev, "streams 0x%llx already enabled on %s:%u\n",
> > > >> enabled_streams, sd->entity.name, pad);
> > > >> ret = -EALREADY;
> > > >> goto done;
> > > >> }
> > > >>
> > > >> - dev_dbg(dev, "enable streams %u:%#llx\n", pad, streams_mask);
> > > >> + dev_dbg(dev, "enable streams %s:%u:%#llx\n",
> > > >> + sd->entity.name, pad, streams_mask);
> > > >>
> > > >> already_streaming = v4l2_subdev_is_streaming(sd);
> > > >>
> > > >> @@ -2333,8 +2334,8 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
> > > >> }
> > > >>
> > > >> if (ret) {
> > > >> - dev_dbg(dev, "enable streams %u:%#llx failed: %d\n", pad,
> > > >> - streams_mask, ret);
> > > >> + dev_err(dev, "enable streams %s:%u:%#llx failed: %d\n",
> > > >> + sd->entity.name, pad, streams_mask, ret);
> > > >> goto done;
> > > >> }
> > > >>
> > > >> @@ -2403,20 +2404,21 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
> > > >> &found_streams, &enabled_streams);
> > > >>
> > > >> if (found_streams != streams_mask) {
> > > >> - dev_dbg(dev, "streams 0x%llx not found on %s:%u\n",
> > > >> + dev_err(dev, "streams 0x%llx not found on %s:%u\n",
> > > >> streams_mask & ~found_streams, sd->entity.name, pad);
> > > >> ret = -EINVAL;
> > > >> goto done;
> > > >> }
> > > >>
> > > >> if (enabled_streams != streams_mask) {
> > > >> - dev_dbg(dev, "streams 0x%llx already disabled on %s:%u\n",
> > > >> + dev_err(dev, "streams 0x%llx already disabled on %s:%u\n",
> > > >> streams_mask & ~enabled_streams, sd->entity.name, pad);
> > > >> ret = -EALREADY;
> > > >> goto done;
> > > >> }
> > > >>
> > > >> - dev_dbg(dev, "disable streams %u:%#llx\n", pad, streams_mask);
> > > >> + dev_dbg(dev, "disable streams %s:%u:%#llx\n",
> > > >> + sd->entity.name, pad, streams_mask);
> > > >>
> > > >> if (!use_s_stream) {
> > > >> /* Call the .disable_streams() operation. */
> > > >> @@ -2432,8 +2434,8 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
> > > >> }
> > > >>
> > > >> if (ret) {
> > > >> - dev_dbg(dev, "disable streams %u:%#llx failed: %d\n", pad,
> > > >> - streams_mask, ret);
> > > >> + dev_err(dev, "disable streams %s:%u:%#llx failed: %d\n",
> > > >> + sd->entity.name, pad, streams_mask, ret);
> > > >> goto done;
> > > >> }
> > > >>
--
Regards,
Laurent Pinchart
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