linux-kernel - Re: [PATCH 3/5] i2c: i2c-stm32f7: add driver

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Message-ID: <CAOAejn0ScANyMEWnBfe0G8xQ5TbR-XYwEdXLkNexqC=AigBNJA@mail.gmail.com>
Date:   Fri, 17 Mar 2017 16:35:20 +0100
From:   "M'boumba Cedric Madianga" <cedric.madianga@...il.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Pierre-Yves MORDRET <pierre-yves.mordret@...com>,
        Russell King <linux@...linux.org.uk>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] i2c: i2c-stm32f7: add driver

> Sorry I don't understand.
> The value you use from the DT and the one calculated from the setup/hold/high/low value
> with the algorithm I developed will set the same values.

With the ST tool, I could set the following values:
I2C speed mode (Master, Fast Mode, Fast Mode Plus)
I2C speed frequency
I2C clock source frequency
I2C rise time
I2C fall time

The values set in the DT in this patchset is 0x40202537 for the
following input values:
I2C speed mode  = Master mode
I2C speed frequency= 100 kHz
I2C clock source frequency = 48 MHz
I2C rise time = 25 ns
I2C fall time = 10 ns

If I keep all the above values and just change I2C rise time with 100
ns, I will have TIMINGR value at 0x10805E89

>
> The main difference is that you won't need the ST tool to calculate these, and even better
> you can provide generic binding for whatever APB frequency the I2C peripheral is running
> on.

As, I2C rise/fall time have some impacts in I2C timings value, the
question is: it is very relevant to let customer control these
parameters ?
If the answer is NO, I agree with you, it is better to use your
formula and remove this property from DT.
If the answer is YES, I think we should keep ST tool.

> Having the STM32L4 running mainline won't be hard, maybe useless, but not hard.
> My point is that you can somehow consider the STM32F0/F1/F4 I2C IP to be "v1" or "gen1",
> and the L0/L4/F6 (and H7 ?) to be "v2" or "gen2" then prepend a generic compatible to
> have something like :
> compatible = "st,stm32-i2c-v2", "st,stm32f7-i2c"

This is not the strategy chosen by the company.
They decided to push all driver with ip_name-stm32.c if the driver is
common for all Soc.
If it not the case, the suffix to be used is the name of the first
supported SoC that introduced the IP in the mainline kernel.

BR,
Cedric