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

[Lars-Peter Clausen]

On 5/11/20 4:56 PM, Ardelean, Alexandru wrote:
> On Mon, 2020-05-11 at 15:58 +0200, Lars-Peter Clausen wrote:
> > [External]
> >
> > On 5/11/20 3:24 PM, Ardelean, Alexandru wrote:
> > > On Mon, 2020-05-11 at 13:03 +0000, Ardelean, Alexandru wrote:
> > > > [External]
> > > >
> > > > 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?
> > > What I should have highlighted [before] with this, is that there is no
> > > devnode()
> > > callback for the bus_type [type].
> > But there is one in device_type :)
> Many thanks :)
> That worked nicely.
>
> I now have:
>
> root@analog:~# ls /dev/iio/*
> /dev/iio/iio:device0  /dev/iio/iio:device1
>
> /dev/iio/device3:
> buffer0  buffer1  buffer2  buffer3
>
> /dev/iio/device4:
> buffer0
>
>
> It looks like I can shift these around as needed.
> This is just an experiment.
> I managed to move the iio devices under /dev/iio, though probably the IIO
> devices will still be around as /dev/iio:deviceX for legacy reasons.
>
> Two things remain unresolved.
> 1. The name of the IIO buffer device.
>
> root@analog:/sys/bus/iio/devices# ls iio\:device3/
> buffer          in_voltage0_test_mode           name
> events          in_voltage1_test_mode           of_node
> iio:buffer:3:0  in_voltage_sampling_frequency   power
> iio:buffer:3:1  in_voltage_scale                scan_elements
> iio:buffer:3:2  in_voltage_scale_available      subsystem
> iio:buffer:3:3  in_voltage_test_mode_available  uevent
>
>
> Right now, each buffer device is named 'iio:buffer:X:Y'.
> One suggesttion was  'iio:deviceX:bufferY'
> I'm suspecting the latter is preferred as when you sort the folders, buffers
> come right after the iio:deviceX folders in /sys/bus/iio/devices.
>
> I don't feel it matters much the device name of the IIO buffer if we symlink it
> to a shorter form.
>   
> I'm guessing, we symlink these devices to short-hand 'bufferY' folders in each
> 'iio:deviceX'?

I think that would be a bit excessive. Only for the legacy buffer we 
need to have a symlink.

> [...]
> 2. I know this is [still] stupid now; but any suggestions one how to symlink
> /dev/iio:device3 -> /dev/iio/device3/buffer0 ?
Does not seem to be possible. Userspace will have to take care of it. 
This means we need to keep legacy devices in /dev/ and only new buffers 
in /dev/iio/.