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From: Arnd Bergmann <arnd@arndb.de>
To: Vitor Soares <Vitor.Soares@synopsys.com>
Cc: 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 5/5] i3c: add i3cdev module to expose i3c dev in /dev
Date: Wed, 11 Dec 2019 16:33:24 +0100
Message-ID: <CAK8P3a2vRG9uiY6jCRip98DHVP5-FeWk_sToGrPSA_WcY0agcA@mail.gmail.com> (raw)
In-Reply-To: <CH2PR12MB4216CE03448AF3B39C23D3BCAE5A0@CH2PR12MB4216.namprd12.prod.outlook.com>

On Wed, Dec 11, 2019 at 4:07 PM Vitor Soares <Vitor.Soares@synopsys.com> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> Date: Tue, Dec 10, 2019 at 19:37:14
> > On Tue, Dec 10, 2019 at 8:15 PM Vitor Soares <Vitor.Soares@synopsys.com> wrote:
> > > From: Arnd Bergmann <arnd@arndb.de>
> > > Date: Tue, Dec 10, 2019 at 17:51:14
> > > > On Tue, Dec 10, 2019 at 4:37 PM Vitor Soares <Vitor.Soares@synopsys.com> wrote:
> > As your interface is basically just read/write based, I wonder
> > if there is a way to completely avoid the ioctl and instead
> > use io_submit() as the primary interface.
>
> I confess that I wasn't familiar with io_submit() until now and went
> straightway for the ioctl() approach.
> So far, my understanding is that io_submit() will call .write or .read of
> i3cdev module depending on the iocb command. if so, we won't be able to
> do a repeated start between a multiple iocb in the same list, right?

I'm not sure what you mean with "repeated start", but it's definitely
possible that io_submit() is not a useful interface for i3c. The main
advantage would be that it avoids creating a complex ioctl command.

> Apart from this private read/write need, another requirement that leads
> me to use the ioctl() was:
> - When we support HDR command in i3c subsystem we can expand the ioctl()
> command to support it.
> - For now, device API doesn't expose CCC commands but some of them are
> used for a private contract between master and device and we likely need
> that support in the future as well.

I think you could still have both the io_submit() interface for basic I/O
(if you can get it to do what you want), plus an ioctl interface for more
complex interactions.

     Arnd

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Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-10 15:37 [RFC 0/5] Introduce i3c device userspace interface Vitor Soares
2019-12-10 15:37 ` [RFC 1/5] i3c: master: export i3c_masterdev_type Vitor Soares
2019-12-10 15:37 ` [RFC 2/5] i3c: master: export i3c_bus_type symbol Vitor Soares
2019-12-10 15:37 ` [RFC 3/5] i3c: device: expose transfer strutures to uapi Vitor Soares
2019-12-12 14:42   ` Greg KH
2019-12-12 14:48     ` Vitor Soares
2019-12-10 15:37 ` [RFC 4/5] i3c: master: add i3c_for_each_dev helper Vitor Soares
2019-12-10 15:37 ` [RFC 5/5] i3c: add i3cdev module to expose i3c dev in /dev Vitor Soares
2019-12-10 17:51   ` Arnd Bergmann
2019-12-10 19:15     ` Vitor Soares
2019-12-10 19:37       ` Arnd Bergmann
2019-12-11 15:07         ` Vitor Soares
2019-12-11 15:33           ` Arnd Bergmann [this message]
2019-12-20 12:39     ` Vitor Soares
2019-12-12 14:44   ` Greg KH
2019-12-12 14:56     ` Vitor Soares
2019-12-12 16:00       ` Greg KH
2019-12-12 17:25         ` Vitor Soares
2019-12-12 17:32           ` Greg KH
2019-12-12 14:46   ` Greg KH

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