linux-kernel - Re: [PATCH] i2c-axxia: support slave mode

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Message-ID: <20190807070926.GB17104@localhost.localdomain>
Date:   Wed, 7 Aug 2019 07:09:32 +0000
From:   "Adamski, Krzysztof (Nokia - PL/Wroclaw)" 
        <krzysztof.adamski@...ia.com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
Subject: Re: [PATCH] i2c-axxia: support slave mode

Hi Wolfram,

>Hi Krzysztof,
>
>> +	if (fifo_status & SLV_FIFO_DV1) {
>> +		if (fifo_status & SLV_FIFO_STRC) {
>> +			dev_dbg(dev, "First data byte sent\n");
>
>I think, however, these debug messages could go. They were surely
>helpful during development but assuming things work now, they will not
>help backend authors. Can you agree?

Good point. I'll remove those verbose messages and maybe leave one or
two debug messages with just a summary of the status which will
hopefully be a good compromise. Will that be ok?

>
>Rest looks good from what I can tell without knowing the hardware.

It also seems to work correctly and I tried to do everything in a way
that nothing is changed if slave mode is not used to eliminate the risk
of regressions.

BTW, I have added this synchronize_irq() in unreg_slave callback just to
make sure it is save to set idev->slave to NULL already. Most of the
controllers do not have such a guard and I'm wondering why that wouldn't
be a problem for them. Like the i2c-rcar.c - isn't there a small race
condition if some slave interrupt triggers just before ICSIER is cleared
and somehow does not finish before priv->slave is set to NULL? This is
the situation I was afraid of and tried to solve by using this
synchronize_irq().

Krzysztof