Re: [PATCH v2 1/1] tty: i3c: add TTY over I3C master support

From: Frank Li <Frank.li@nxp.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: alexandre.belloni@bootlin.com, conor.culhane@silvaco.com,
	imx@lists.linux.dev, jirislaby@kernel.org, joe@perches.com,
	linux-i3c@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-serial@vger.kernel.org, miquel.raynal@bootlin.com
Subject: Re: [PATCH v2 1/1] tty: i3c: add TTY over I3C master support
Date: Tue, 24 Oct 2023 12:04:40 -0400	[thread overview]
Message-ID: <ZTfrGAyf194yxX4q@lizhi-Precision-Tower-5810> (raw)
In-Reply-To: <ZTfp+c60YOiwDUFd@lizhi-Precision-Tower-5810>

On Tue, Oct 24, 2023 at 11:59:53AM -0400, Frank Li wrote:
> On Tue, Oct 24, 2023 at 05:05:47PM +0200, Greg KH wrote:
> > On Tue, Oct 24, 2023 at 10:31:51AM -0400, Frank Li wrote:
> > > On Tue, Oct 24, 2023 at 11:30:33AM +0200, Greg KH wrote:
> > > > On Mon, Oct 23, 2023 at 12:26:42PM -0400, Frank Li wrote:
> > > > > On Sat, Oct 21, 2023 at 07:02:40PM +0200, Greg KH wrote:
> > > > > > Note, your subject line needs to change.
> > > > > > 
> > > > > > On Fri, Oct 20, 2023 at 12:00:27PM -0400, Frank Li wrote:
> > > > > > > In typical embedded Linux systems, UART consoles require at least two pins,
> > > > > > > TX and RX. In scenarios where I2C/I3C devices like sensors or PMICs are
> > > > > > > present, we can save these two pins by using this driver. Pins is crucial
> > > > > > 
> > > > > > "Pins are crucial"
> > > > > > 
> > > > > > > resources, especially in small chip packages.
> > > > > > > 
> > > > > > > This introduces support for using the I3C bus to transfer console tty data,
> > > > > > > effectively replacing the need for dedicated UART pins. This not only
> > > > > > > conserves valuable pin resources but also facilitates testing of I3C's
> > > > > > > advanced features, including early termination, in-band interrupt (IBI)
> > > > > > > support, and the creation of more complex data patterns. Additionally,
> > > > > > > it aids in identifying and addressing issues within the I3C controller
> > > > > > > driver.
> > > > > > 
> > > > > > But where is the serial data ending up at?  Not a normal uart, what is
> > > > > > on the other end?  And do line settings mean anything here?
> > > > > 
> > > > > Currently, it use slave i3c code. 
> > > > > https://lore.kernel.org/imx/20231018215809.3477437-1-Frank.Li@nxp.com/T/#t
> > > > > 
> > > > > idealy build an i3c->usb dongle to bride it to usb acm. 
> > > > 
> > > > So no one has built such a thing yet to determine if any of this works?
> > > 
> > > It is easy to proof concept by I3C slave code and USB gadget ACM, then pipe
> > > two tty (ttyACM0 and ttySI3C0 together).
> > 
> > So you have not actually tested this?  why write a driver that no one is
> > using?
> 
> I3c slave side tty at
> https://lore.kernel.org/imx/20231018215809.3477437-1-Frank.Li@nxp.com/T/#t
> 
> I just have not tested tty to USB part. This patch is major for tty -> i3c
> master -> i3c taret -> tty now.
> 
> As my previous said, two major purpose now. 
> 1. Save two pads.
> 2. Test i3c master and i3c target driver. I3C target driver frame was
> written by me and posted. It needs a driver to verify it works. In stead of
> write a test driver (such as i2c slave, pci-endpoint), it is better to
> write an actual function driver, such as tty. It can exchange message
> between two boards, which connected by SDA/SCL.
> 
> Frank
> > 
> > > Of we also can implement a USB to I3C class standard, base on this, reuse
> > > this tty driver at host side.
> > 
> > Is there a USB I3C standard?  I see i3c descriptors assigned by the
> > USB-IF, but haven't dug to see if there's more than that anywhere...

Sorry, forget answer this quesiton. Yes, it is standard class. Spec is in
usb.org. I have not found actual usage mode yet. 

> > 
> > thanks,
> > 
> > greg k-h

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