linux-kernel - Re: [PATCH 3/7] media: imx274: don't hard-code the subdev name to DRIVER

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Date:   Tue, 28 Aug 2018 18:02:55 +0200
From:   Philippe De Muyter <phdm@...q.eu>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Luca Ceresoli <luca@...aceresoli.net>,
        Sakari Ailus <sakari.ailus@....fi>,
        linux-media@...r.kernel.org, Leon Luo <leonl@...pardimaging.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-kernel@...r.kernel.org, laurent.pinchart@...asonboard.com
Subject: Re: [PATCH 3/7] media: imx274: don't hard-code the subdev name to
        DRIVER_NAME

Hi Hans, Sakari and Luca

On Tue, Aug 28, 2018 at 11:22:28AM +0200, Hans Verkuil wrote:
> On 26/08/18 22:41, Luca Ceresoli wrote:
> > Hi Sakari,
> > 
> > On 25/08/2018 16:49, Sakari Ailus wrote:
> >> Hi Luca,
> >>
> >> On Fri, Aug 24, 2018 at 06:35:21PM +0200, Luca Ceresoli wrote:
> >>> 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@...aceresoli.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.
> > 
> >> 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.
> > 
> >> 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/

Philippe

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