Re: [RFC PATCH 00/14] iio: buffer: add support for multiple buffers

[Ardelean, Alexandru]

On Mon, 2020-05-11 at 12:37 +0200, Lars-Peter Clausen wrote:
> [External]
> 
> On 5/11/20 12:33 PM, Ardelean, Alexandru wrote:
> > On Sun, 2020-05-10 at 11:09 +0100, Jonathan Cameron wrote:
> > > [External]
> > > 
> > > On Sat, 9 May 2020 10:52:14 +0200
> > > Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
> > > 
> > > > On 5/8/20 3:53 PM, Alexandru Ardelean wrote:
> > > > > [...]
> > > > > What I don't like, is that iio:device3 has iio:buffer3:0 (to 3).
> > > > > This is because the 'buffer->dev.parent = &indio_dev->dev'.
> > > > > But I do feel this is correct.
> > > > > So, now I don't know whether to leave it like that or symlink to
> > > > > shorter
> > > > > versions like 'iio:buffer3:Y' -> 'iio:device3/bufferY'.
> > > > > The reason for naming the IIO buffer devices to 'iio:bufferX:Y' is
> > > > > mostly to make the names unique. It would have looked weird to do
> > > > > '/dev/buffer1' if I would have named the buffer devices 'bufferX'.
> > > > > 
> > > > > So, now I'm thinking of whether all this is acceptable.
> > > > > Or what is acceptable?
> > > > > Should I symlink 'iio:device3/iio:buffer3:0' -> 'iio:device3/buffer0'?
> > > > > What else should I consider moving forward?
> > > > > What means forward?
> > > > > Where did I leave my beer?
> > > > Looking at how the /dev/ devices are named I think we can provide a name
> > > > that is different from the dev_name() of the device. Have a look at
> > > > device_get_devnode() in drivers/base/core.c. We should be able to
> > > > provide the name for the chardev through the devnode() callback.
> > > > 
> > > > While we are at this, do we want to move the new devices into an iio
> > > > subfolder? So iio/buffer0:0 instead of iio:buffer0:0?
> > > Possibly on the folder.  I can't for the life of me remember why I decided
> > > not to do that the first time around - I'll leave it at the
> > > mysterious "it may turn out to be harder than you'd think..."
> > > Hopefully not ;)
> > I was also thinking about the /dev/iio subfolder while doing this.
> > I can copy that from /dev/input
> > They seem to do it already.
> > I don't know how difficult it would be. But it looks like a good precedent.
> 
> All you have to do is return "iio/..." from the devnode() callback.

I admit I did not look closely into drivers/input/input.c before mentioning this
as as good precedent.

But, I looks like /dev/inpput is a class.
While IIO devices are a bus_type devices.
Should we start implementing an IIO class? or?


> 
> > My concern regarding going to use stuff from core [like
> > device_get_devnode()] is
> > that it seems to bypass some layers of kernel.
> > If I do 'git grep device_get_devnode', I get:
> > 
> > drivers/base/core.c:            name = device_get_devnode(dev, &mode, &uid,
> > &gid, &tmp);
> > drivers/base/core.c: * device_get_devnode - path of device node file
> > drivers/base/core.c:const char *device_get_devnode(struct device *dev,
> > drivers/base/devtmpfs.c:        req.name = device_get_devnode(dev,
> > &req.mode,
> > &req.uid, &req.gid, &tmp);
> > drivers/base/devtmpfs.c:        req.name = device_get_devnode(dev, NULL,
> > NULL,
> > NULL, &tmp);
> > include/linux/device.h:extern const char *device_get_devnode(struct device
> > *dev,
> > (END)
> > 
> > So, basically, most uses of device_get_devnode() are in core code, and I
> > feel
> > that this may be sanctioned somewhere by some core people, if I do it.
> > I could be wrong, but if you disagree, I'll take your word for it.
> You are not supposed to use the function itself, you should implement 
> the devnode() callback for the IIO bus, which is then used by the core 
> device_get_devnode() function.
>