linux-kernel - Re: [PATCH v3 01/12] scripts/dtc: check: Add 10bit/slave i2c reg flags support

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Date:   Wed, 27 May 2020 12:46:04 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Rob Herring <robh@...nel.org>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Frank Rowand <frowand.list@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        <linux-mips@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 01/12] scripts/dtc: check: Add 10bit/slave i2c reg
 flags support

On Tue, May 26, 2020 at 07:17:04PM -0600, Rob Herring wrote:
> On Wed, May 27, 2020 at 12:55:17AM +0300, Serge Semin wrote:
> > Recently the I2C-controllers slave interface support was added to the
> > kernel I2C subsystem. In this case Linux can be used as, for example,
> > a I2C EEPROM machine. See [1] for details. Other than instantiating
> > the EEPROM-slave device from user-space there is a way to declare the
> > device in dts. In this case firstly the I2C bus controller must support
> > the slave interface. Secondly I2C-slave sub-node of that controller
> > must have "reg"-property with flag I2C_OWN_SLAVE_ADDRESS set (flag is
> > declared in [2]). That flag is declared as (1 << 30), which when set
> > makes dtc unhappy about too big address set for a I2C-slave:
> > 
> > Warning (i2c_bus_reg): /example-2/i2c@...0000/eeprom@64: I2C bus unit address format error, expected "40000064"
> > Warning (i2c_bus_reg): /example-2/i2c@...0000/eeprom@64:reg: I2C address must be less than 10-bits, got "0x40000064"
> > 
> > Similar problem would have happened if we had set the 10-bit address
> > flag I2C_TEN_BIT_ADDRESS in the "reg"-property.
> > 
> > In order to fix the problem we suggest to alter the I2C-bus reg-check
> > algorithm, so one would be aware of the upper bits set. Normally if no
> > flag specified, the 7-bit address is expected in the "reg"-property.
> > If I2C_TEN_BIT_ADDRESS is set, then the 10-bit address check will be
> > performed. The I2C_OWN_SLAVE_ADDRESS flag will be just ignored.
> > 
> > [1] Documentation/i2c/slave-interface.rst
> > [2] include/dt-bindings/i2c/i2c.h
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> > Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> > Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > Cc: linux-mips@...r.kernel.org
> > Cc: linux-i2c@...r.kernel.org
> > ---
> >  scripts/dtc/checks.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> 

> I've lost track of who all I've said this to already for this issue, but 
> patches to dtc should be against upstream and a version of this has been 
> sent there already. But it seems they've lost interest in addressing the 
> review comments. So feel free to send another one. The same comment 
> applies here.

Agreed. Rob, could you also take a look at the patch
[PATCH v3 03/12] dt-bindings: i2c: Discard i2c-slave flag from the DW I2C example
from this series? You must have missed that. I've created that patch in
accordance with your suggestion from v2:
https://lore.kernel.org/linux-i2c/20200511160924.GA9628@bogus/

-Sergey

> 
> Rob