linux-kernel - RE: [RFC v2 0/4] Introduce i3c device userspace interface

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Message-ID: <CH2PR12MB4216459E37F9AB1AAF0B2EFDAE160@CH2PR12MB4216.namprd12.prod.outlook.com>
Date:   Mon, 17 Feb 2020 15:32:55 +0000
From:   Vitor Soares <Vitor.Soares@...opsys.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "bbrezillon@...nel.org" <bbrezillon@...nel.org>,
        "broonie@...nel.org" <broonie@...nel.org>
Subject: RE: [RFC v2 0/4] Introduce i3c device userspace interface

Hi Boris,

From: Boris Brezillon <boris.brezillon@...labora.com>
Date: Mon, Feb 17, 2020 at 14:51:41

> Hello Vitor,
> 
> Sorry for taking so long to reply, and thanks for working on that topic.
> 
> On Wed, 29 Jan 2020 13:17:31 +0100
> Vitor Soares <Vitor.Soares@...opsys.com> wrote:
> 
> > For today there is no way to use i3c devices from user space and
> > the introduction of such API will help developers during the i3c device
> > or i3c host controllers development.
> > 
> > The i3cdev module is highly based on i2c-dev and yet I tried to address
> > the concerns raised in [1].
> > 
> > NOTES:
> > - The i3cdev dynamically request an unused major number.
> > 
> > - The i3c devices are dynamically exposed/removed from dev/ folder based
> >   on if they have a device driver bound to it.
> 
> May I ask why you need to automatically bind devices to the i3cdev
> driver when they don't have a driver matching the device id
> loaded/compiled-in? If we get the i3c subsystem to generate proper
> uevents we should be able to load the i3cdev module and bind the device
> to this driver using a udev rule.

My idea was to expose every device to user-space by default so we can 
test them without a driver (more or less the i2c use case) but as we 
agreed during the i3c subsystem only expose devices that doesn't have 
device driver.
I considered to have a uevent but to expose the devices by default it 
would required something generic, what I didn't figure out and tend to 
follow the i2c-dev module.

With this current approach even if a device has a driver we can unbind it 
through the Sysfs and have access from user space which I found useful 
for debug.

> 
> Regards,
> 
> Boris