linux-kernel - Re: [PATCH 4/4] i2c: stm32f7: Add SMBus-specific protocols support

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Date:   Tue, 26 May 2020 12:39:38 +0200
From:   Alain Volmat <alain.volmat@...com>
To:     Wolfram Sang <wsa@...nel.org>
CC:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <pierre-yves.mordret@...com>, <mcoquelin.stm32@...il.com>,
        <alexandre.torgue@...com>, <linux-i2c@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <fabrice.gasnier@...com>
Subject: Re: [PATCH 4/4] i2c: stm32f7: Add SMBus-specific protocols support

On Sat, May 23, 2020 at 01:01:40PM +0200, Wolfram Sang wrote:
> 
> > +static int stm32f7_i2c_reg_client(struct i2c_client *client)
> > +{
> > +	struct stm32f7_i2c_dev *i2c_dev = i2c_get_adapdata(client->adapter);
> > +	int ret;
> > +
> > +	if (client->flags & I2C_CLIENT_HOST_NOTIFY) {
> > +		/* Only enable on the first device registration */
> > +		if (atomic_inc_return(&i2c_dev->host_notify_cnt) == 1) {
> > +			ret = stm32f7_i2c_enable_smbus_host(i2c_dev);
> > +			if (ret) {
> > +				dev_err(i2c_dev->dev,
> > +					"failed to enable SMBus host notify (%d)\n",
> > +					ret);
> > +				return ret;
> > +			}
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> 
> So, as mentioned in the other review, I'd like to evaluate other
> possibilities for the above:
> 
> - One option is to enable it globally in probe(). Then you lose the
>   possibility to have a device at address 0x08.

I'd prefer avoid this solution to not lose the address 0x08.

> - Enable it in probe() only if there is a generic binding "host-notify".

Do you mean having the adapter walk through childs node and see if at least
one of them have the host-notify property ? This mean that such solution
wouldn't work for device relying on platform data rather than DT nodes.

> - Let the core scan for a device with HOST_NOTIFY when registering an
>   adapter and then call back into the driver somehow?

You mean at adapter registration time only ? Not device probing time ?
At probing time, we could have the core (i2c_device_probe) check for the flag
HOST_NOTIFY and if setted call a dedicated host-notify reg callback ?

> 
> Other ideas?
>