linux-kernel - Re: [RESEND PATCH v1 2/6] i2c: i2c-stm32f7: Add slave support

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Date:   Tue, 20 Mar 2018 11:17:21 +0100
From:   Pierre Yves MORDRET <pierre-yves.mordret@...com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        <linux-i2c@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v1 2/6] i2c: i2c-stm32f7: Add slave support



On 03/20/2018 10:52 AM, Wolfram Sang wrote:
> 
>> I do believe the hw can support it, even it looks odd to me having the same I2C
>> in slave and master mode at the same time.
> 
> I2C is multi-master, so it is perfectly valid for a device to be master
> and slave. I do have seen designs making use of that more than once.
> 
>> Nevertheless the driver is devised to support either master or slave more but
>> not at the same time.
> 
> Why should we limit ourselves here? Also, why should we have an
> unnecessary configuration option?
> 
> Unless the HW is broken and does not support it, I usually don't accept
> slave-only solutions. If the needs for master and slave arises later,
> this is hard to refactor and better done properly right away.
> 
> Is it so hard? Usually you have irqs for master and for slave seperated,
> so you can code things quite orthogonal. Check de20d1857dd6 ("i2c: rcar:
> add slave support") as an example.
> 

I need to check at my end but status bits are shared between master and slave in
my IP: i.e. Tx Empty, Rx Empty, NAxk, Stop.
Both bits have a meaning in either master and slave mode. In your case status
bits are separated between master and slave.
BTW I need to think about it.