linux-kernel - Re: [EXT] Re: [PATCH 1/2] i2c: imx: I2C Driver doesn't consider I2C_IPGCLK

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Date:   Thu, 9 May 2019 09:55:28 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     Sumit Batra <sumit.batra@....com>,
        Chuanhua Han <chuanhua.han@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "wsa+renesas@...g-engineering.com" <wsa+renesas@...g-engineering.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "eha@...f.com" <eha@...f.com>,
        "linux@...pel-privat.de" <linux@...pel-privat.de>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "peda@...ntia.se" <peda@...ntia.se>
Subject: Re: [EXT] Re: [PATCH 1/2] i2c: imx: I2C Driver doesn't consider
 I2C_IPGCLK_SEL RCW bit when using ls1046a SoC


> > There are 2 places where clock division takes place -
> > 
> > 1) There is a clock divider outside of I2C block, which makes the clock reaching
> >    I2C module as - Platform Clock/2
> > 2) There is another clock divider which specifically divides the clock to the I2C block,
> >    based on RCW bit 424 (if 424th bit is 0 then the baud clock source is Platform Clock/4,
> >    if 424th bit is 1 then it remains Platform Clock/2)
> 
> So there is a clock divider which based on RCW bit 424 divides the clock
> *to* the i2c module. This suggests the divider is outside of the i2c
> module itself and thus part of the clock module.
> 
> We could argue that this divider sits between the clock module and the
> i2c module, but for sure it's not in the i2c module. I really suggest to
> put this SoC specific into the SoC specific clock driver rather than
> littering the i2c driver with it.

I am with Sascha here. The fact that you need to of_ioremap some
registers is a really strong indication that the code should go
somewhere else. I can't tell the best place (clock driver or seperate
GUTS driver or syscon driver), but the I2C bus driver seems not
suitable.


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