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Subject: Re: [PATCH net-next v2 01/13] net: phy: sfp: make the i2c-bus
 property really optional
To:     Antoine Tenart <antoine.tenart@bootlin.com>, davem@davemloft.net,
        kishon@ti.com, linux@armlinux.org.uk, gregory.clement@bootlin.com,
        andrew@lunn.ch, jason@lakedaemon.net,
        sebastian.hesselbarth@gmail.com
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        thomas.petazzoni@bootlin.com, maxime.chevallier@bootlin.com,
        miquel.raynal@bootlin.com, nadavh@marvell.com, stefanc@marvell.com,
        ymarkman@marvell.com, mw@semihalf.com,
        linux-arm-kernel@lists.infradead.org
References: <20180504135643.23466-1-antoine.tenart@bootlin.com>
 <20180504135643.23466-2-antoine.tenart@bootlin.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
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Message-ID: <fd91699d-c290-8821-b4a6-0789071cfba1@gmail.com>
Date:   Fri, 4 May 2018 10:03:16 -0700
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On 05/04/2018 06:56 AM, Antoine Tenart wrote:
> The SFF,SFP documentation is clear about making all the DT properties,
> with the exception of the compatible, optional. In practice this is not
> the case and without an i2c-bus property provided the SFP code will
> throw NULL pointer exceptions.
> 
> This patch is an attempt to fix this.
> 
> Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
> ---
>  drivers/net/phy/sfp.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
> index 4ab6e9a50bbe..4686c443fc22 100644
> --- a/drivers/net/phy/sfp.c
> +++ b/drivers/net/phy/sfp.c
> @@ -298,11 +298,17 @@ static void sfp_set_state(struct sfp *sfp, unsigned int state)
>  
>  static int sfp_read(struct sfp *sfp, bool a2, u8 addr, void *buf, size_t len)
>  {
> +	if (!sfp->read)
> +		return -EOPNOTSUPP;

-ENODEV would be closer to the intended meaning IMHO, those this could
be argue that this is yet another color to paint the bikeshed with.

> +
>  	return sfp->read(sfp, a2, addr, buf, len);
>  }
>  
>  static int sfp_write(struct sfp *sfp, bool a2, u8 addr, void *buf, size_t len)
>  {
> +	if (!sfp->write)
> +		return -EOPNOTSUPP;
> +
>  	return sfp->write(sfp, a2, addr, buf, len);
>  }
>  
> @@ -533,6 +539,8 @@ static int sfp_sm_mod_hpower(struct sfp *sfp)
>  		return 0;
>  
>  	err = sfp_read(sfp, true, SFP_EXT_STATUS, &val, sizeof(val));
> +	if (err == -EOPNOTSUPP)
> +		goto err;
>  	if (err != sizeof(val)) {
>  		dev_err(sfp->dev, "Failed to read EEPROM: %d\n", err);
>  		err = -EAGAIN;
> @@ -542,6 +550,8 @@ static int sfp_sm_mod_hpower(struct sfp *sfp)
>  	val |= BIT(0);
>  
>  	err = sfp_write(sfp, true, SFP_EXT_STATUS, &val, sizeof(val));
> +	if (err == -EOPNOTSUPP)
> +		goto err;
>  	if (err != sizeof(val)) {
>  		dev_err(sfp->dev, "Failed to write EEPROM: %d\n", err);
>  		err = -EAGAIN;
> @@ -565,6 +575,8 @@ static int sfp_sm_mod_probe(struct sfp *sfp)
>  	int ret;
>  
>  	ret = sfp_read(sfp, false, 0, &id, sizeof(id));
> +	if (ret == -EOPNOTSUPP)
> +		return ret;

Can you find a way such that only sfp_sm_mod_probe() needs to check
whether the sfp read/write operations returned failure and then we just
make sure the SFP state machine does not make any more progress? Having
to check the sfp_read()/sfp_write() operations all over the place sounds
error prone and won't scale in the future.
-- 
Florian