linux-kernel - Re: [PATCH v5 4/6] i2c: designware: Implement I2C_M

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Message-ID: <7226044.9J7NaK4W3v@benoit.monin>
Date: Fri, 23 Jan 2026 15:25:24 +0100
From: Benoît Monin <benoit.monin@...tlin.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Andi Shyti <andi.shyti@...nel.org>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 Jan Dabros <jsd@...ihalf.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Gregory CLEMENT <gregory.clement@...tlin.com>,
 Théo Lebrun <theo.lebrun@...tlin.com>,
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>,
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>,
 Dmitry Guzman <dmitry.guzman@...ileye.com>, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH v5 4/6] i2c: designware: Implement I2C_M_STOP support

On Thursday, 22 January 2026 at 17:25:58 CET, Andy Shevchenko wrote:
> On Tue, Jan 20, 2026 at 10:28:04AM +0100, Benoît Monin wrote:
> > Add the support of the I2C_M_STOP flag in i2c_msg by splitting
> > i2c_dw_xfer() in two: __i2c_dw_xfer_one_part() for the core transfer logic
> > and i2c_dw_xfer() for handling the high-level transaction management.
> > 
> > In detail __i2c_dw_xfer_one_part() starts a transaction and wait for its
> > completion, either with a STOP on the bus or an error. i2c_dw_xfer()
> > loops over the messages to search for the I2C_M_STOP flag and calls
> > __i2c_dw_xfer_one_part() for each part of the messages up to a STOP or
> > the end of the messages array.
> > 
> > i2c_dw_xfer() takes care of runtime PM and holds the hardware lock on
> > the bus while calling __i2c_dw_xfer_one_part(), this allows grouping
> > multiple accesses to device that support a STOP in a transaction when
> > done via i2c_dev I2C_RDWR ioctl.
> 
> Does i2c-tools support this. I.o.w. can you put an example of user space call
> to achieve the above?
> 
I posted a patch series for i2c-tools, adding support for message modifier
flags including I2C_M_STOP to i2ctransfer:
https://lore.kernel.org/all/20251223-msg-flags-v2-0-8d934a4366e2@bootlin.com/

I am working on version 3, following Jean and Wolfram's reviews.

[...]

Thanks for the review!
-- 
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com