Hi Sakari,

On Wed, Aug 29, 2018 at 02:07:21PM +0300, Sakari Ailus wrote:

Hi Philippe,

On Tue, Aug 28, 2018 at 06:02:55PM +0200, Philippe De Muyter wrote:

quoted

Hi Hans, Sakari and Luca

On Tue, Aug 28, 2018 at 11:22:28AM +0200, Hans Verkuil wrote:

quoted

On 26/08/18 22:41, Luca Ceresoli wrote:

quoted

Hi Sakari,

On 25/08/2018 16:49, Sakari Ailus wrote:

quoted

Hi Luca,

On Fri, Aug 24, 2018 at 06:35:21PM +0200, Luca Ceresoli wrote:

quoted

Forcibly setting the subdev name to DRIVER_NAME (i.e. "IMX274") makes
it non-unique and less informative.

Let the driver use the default name from i2c, e.g. "IMX274 2-001a".

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
---
 drivers/media/i2c/imx274.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/media/i2c/imx274.c b/drivers/media/i2c/imx274.c
index 9b524de08470..570706695ca7 100644
--- a/drivers/media/i2c/imx274.c
+++ b/drivers/media/i2c/imx274.c

@@ -1885,7 +1885,6 @@ static int imx274_probe(struct i2c_client *client,
 	imx274->client = client;
 	sd = &imx274->sd;
 	v4l2_i2c_subdev_init(sd, client, &imx274_subdev_ops);
-	strlcpy(sd->name, DRIVER_NAME, sizeof(sd->name));
 	sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE | V4L2_SUBDEV_FL_HAS_EVENTS;
 
 	/* initialize subdev media pad */

This ends up changing the entity as well as the sub-device name which may
well break applications.

Right, unfortunately.

quoted

On the other hand, you currently can't have more
than one of these devices on a media device complex due to the name being
specific to a driver, not the device.

An option avoiding that would be to let the user choose by e.g. through a
Kconfig option would avoid having to address that, but I really hate adding
such options.

I agree adding a Kconfig option just for this would be very annoying.
However I think the issue affects a few other drivers (sr030pc30.c and
s5c73m3-core.c apparently), thus maybe one option could serve them all.

quoted

I wonder what others think. If anyone ever needs to add another on a board
so that it ends up being the part of the same media device complex
(likely), then changing the name now rather than later would be the least
pain. In this case I'd be leaning (slightly) towards accepting the patch
and hoping there wouldn't be any fallout... I don't see any board (DT)
containing imx274, at least not in the upstream kernel.

I'll be OK with either decision. Should we keep it as is, then I think a
comment before that line would be appropriate to clarify it's not
correct but it is kept for backward userspace compatibility. This would
help avoid new driver writers doing the same mistake, and prevent other
people to send another patch like mine.

In this end, this is a driver bug. I would just fix this, but add a comment
that states the old name and why it was changed. No need for a dev_info
IMHO.

It would be nice if you can check if the same mistake is made in other drivers,
and update those as well. It's easier if this is all done at the same time.

Then we should probably also apply the following patch I submitted :

"media: v4l2-common: v4l2_spi_subdev_init : generate unique name"
	https://patchwork.kernel.org/patch/10553035/

and perhaps

"media: v4l2-common: simplify v4l2_i2c_subdev_init name generation"
	https://patchwork.kernel.org/patch/10553037/

The problem with this patch is that the existing naming scheme is very
similar while the new one offers no tangible benefits apart from being in
line with the rest of the kernel. That's still not a benefit for uAPI:
changing the name is certain to break user space applications.

I agree with you on the patch for v4l2_i2c_subdev_init (I wrote 'perhaps'),
but you don't say anything on the one about v4l2_spi_subdev_init :), which
fixes an actual bug.  I have 2 identical SPI-controlled sensors on the
same board, and without my patch they get the same subdev name.  Of course,
I could fix that in the sensor driver itself, but that's not what we want,
or do we ?

Best Regards

Philippe

-- 
Philippe De Muyter +32 2 6101532 Macq SA rue de l'Aeronef 2 B-1140 Bruxelles