netdev - Re: [PATCH net-next v4 1/4] net: phy: mdio-i2c: support I2C MDIO protocol for RollBall SFP modules

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Date:   Wed, 13 Jan 2021 11:51:47 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Marek Behún <kabel@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        Russell King <rmk+kernel@...linux.org.uk>,
        Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Subject: Re: [PATCH net-next v4 1/4] net: phy: mdio-i2c: support I2C MDIO
 protocol for RollBall SFP modules

On Tuesday 12 January 2021 22:01:14 Marek Behún wrote:
> On Tue, 12 Jan 2021 21:54:24 +0100
> Andrew Lunn <andrew@...n.ch> wrote:
> 
> > > +static int i2c_transfer_rollball(struct i2c_adapter *i2c,
> > > +				 struct i2c_msg *msgs, int num)
> > > +{
> > > +	u8 saved_page;
> > > +	int ret;
> > > +
> > > +	i2c_lock_bus(i2c, I2C_LOCK_SEGMENT);
> > > +
> > > +	/* save original page */
> > > +	ret = __i2c_rollball_get_page(i2c, msgs->addr, &saved_page);
> > > +	if (ret)
> > > +		goto unlock;
> > > +
> > > +	/* change to RollBall MDIO page */
> > > +	ret = __i2c_rollball_set_page(i2c, msgs->addr, SFP_PAGE_ROLLBALL_MDIO);
> > > +	if (ret)
> > > +		goto unlock;
> > > +
> > > +	/* do the transfer */
> > > +	ret = __i2c_transfer_err(i2c, msgs, num);
> > > +	if (ret)
> > > +		goto unlock;  
> > 
> > If get page and set page worked, and you get an error in during the
> > actual data transfer, i wonder if you should try restoring the page
> > before returning with the error?
> 
> I don't know. Can i2c trasfer fail and the next one succeed?

I guess it can depend also on i2c driver. I'm for trying to restore
previous i2c page on failure. In the worst case also restoring fails...