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From: Vitor Soares <Vitor.Soares@synopsys.com>
To: Boris Brezillon <boris.brezillon@collabora.com>,
	Arnd Bergmann <arnd@arndb.de>
Cc: Jose Abreu <Jose.Abreu@synopsys.com>,
	Joao Pinto <Joao.Pinto@synopsys.com>,
	Wolfram Sang <wsa@the-dreams.de>,
	gregkh <gregkh@linuxfoundation.org>,
	Boris Brezillon <bbrezillon@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Mark Brown <broonie@kernel.org>,
	"linux-i3c@lists.infradead.org" <linux-i3c@lists.infradead.org>
Subject: RE: [RFC v2 0/4] Introduce i3c device userspace interface
Date: Mon, 17 Feb 2020 15:55:08 +0000
Message-ID: <CH2PR12MB42166ED8E84503B53340F80DAE160@CH2PR12MB4216.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20200217163622.6c78fa3f@collabora.com>

Hi,

From: Boris Brezillon <boris.brezillon@collabora.com>
Date: Mon, Feb 17, 2020 at 15:36:22

> On Mon, 17 Feb 2020 16:06:45 +0100
> Arnd Bergmann <arnd@arndb.de> wrote:
> 
> > On Mon, Feb 17, 2020 at 3:51 PM Boris Brezillon
> > <boris.brezillon@collabora.com> wrote:
> > > 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@synopsys.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.  
> > 
> > I think that would require manual configuration to ensure that the correct
> > set of devices get bound to either the userspace driver or an in-kernel
> > driver.
> 
> Hm, isn't that what udev is supposed to do anyway? Remember that
> I3C devices expose a manufacturer and part-id (which are similar to the
> USB vendor and product ids), so deciding when an I3C device should be
> bound to the i3cdev driver should be fairly easy, and that's a
> per-device decision anyway.
> 
> > The method from the current patch series is more complicated,
> > but it means that any device can be accessed by the user space driver
> > as long as it's not already owned by a kernel driver.
> 
> Well, I'm more worried about the extra churn this auto-binding logic
> might create for the common 'on-demand driver loading' use case. At
> first, there's no driver matching a specific device, but userspace
> might load one based on the uevents it receives. With the current
> approach, that means we'd first have to unbind the device before
> loading the driver. AFAICT, no other subsystem does that.

I'm about to finish v3 (today or tomorrow) and I think I fixed all 
concerns rise during v2. I would like you to see that version before any 
change.

Best regards,
Vitor Soares


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Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-29 12:17 Vitor Soares
2020-01-29 12:17 ` [RFC v2 1/4] i3c: master: export i3c_masterdev_type Vitor Soares
2020-02-17 14:56   ` Boris Brezillon
2020-02-17 14:59     ` Boris Brezillon
2020-01-29 12:17 ` [RFC v2 2/4] i3c: master: export i3c_bus_type symbol Vitor Soares
2020-01-29 12:17 ` [RFC v2 3/4] i3c: master: add i3c_for_each_dev helper Vitor Soares
2020-01-29 12:17 ` [RFC v2 4/4] i3c: add i3cdev module to expose i3c dev in /dev Vitor Soares
2020-01-29 14:30   ` Arnd Bergmann
2020-01-29 17:00     ` Vitor Soares
2020-01-29 19:39       ` Arnd Bergmann
2020-02-04 13:19         ` Vitor Soares
2020-02-17 15:26   ` Boris Brezillon
2020-02-17 14:51 ` [RFC v2 0/4] Introduce i3c device userspace interface Boris Brezillon
2020-02-17 15:06   ` Arnd Bergmann
2020-02-17 15:36     ` Boris Brezillon
2020-02-17 15:55       ` Vitor Soares [this message]
2020-02-17 16:03         ` gregkh
2020-02-17 16:12           ` Vitor Soares
2020-02-17 16:23         ` Boris Brezillon
2020-02-17 16:31           ` Arnd Bergmann
2020-02-17 17:06             ` Boris Brezillon
2020-02-17 16:19       ` Arnd Bergmann
2020-02-17 16:34         ` Boris Brezillon
2020-02-17 15:32   ` Vitor Soares
2020-02-17 15:52     ` Boris Brezillon
2020-02-17 17:37   ` Boris Brezillon

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