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

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Message-ID: <9ae7e69b-f4ce-dd2b-d70b-2aac66b19814@metafoo.de>
Date:   Mon, 11 May 2020 15:58:01 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>,
        "jic23@...nel.org" <jic23@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: Re: [RFC PATCH 00/14] iio: buffer: add support for multiple buffers

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@...afoo.de> 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 :)