netdev - Re: [RFC PATCH net-next v3 03/15] net: dsa: mt7530: use regmap to access switch register space

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Message-ID: <e8bb79ab-94d2-4e36-9b75-576a47e6c126@lunn.ch>
Date:   Wed, 29 Mar 2023 21:35:17 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Daniel Golle <daniel@...rotopia.org>
Cc:     netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Sam Shih <Sam.Shih@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        John Crispin <john@...ozen.org>, Felix Fietkau <nbd@....name>
Subject: Re: [RFC PATCH net-next v3 03/15] net: dsa: mt7530: use regmap to
 access switch register space

On Wed, Mar 29, 2023 at 07:33:17PM +0100, Daniel Golle wrote:
> On Wed, Mar 29, 2023 at 06:24:21PM +0200, Andrew Lunn wrote:
> > Thanks for splitting this patchset up. This is much easier to review.
> > 
> > > +static u32
> > > +mt7530_mii_read(struct mt7530_priv *priv, u32 reg)
> > > +{
> > > +	int ret;
> > > +	u32 val;
> > > +
> > > +	ret = regmap_read(priv->regmap, reg, &val);
> > > +	if (ret) {
> > > +		dev_err(priv->dev,
> > > +			"failed to read mt7530 register\n");
> > > +		return ret;
> > 
> > This is a u32 function. ret should be negative on error, which is
> > going to be turned positive in order to return a u32. So you probably
> > want to make this an int function.
> 
> This is a pre-existing flaw in the code. As we are accessing 32-bit
> registers there has just never been any meaningful error handling.

O.K. At least i would not return the negative error code. Return 0, or
0xdeadbeef or something. And consider adding a WARN_ON_ONCE() so it is very loud
when it goes wrong.

> I guess the correct solution would be to not use the return value only
> to indicate success or error, and use an additional u32* parameter for
> the read value.

Yes, that is what mv88e6xxx does.

> However, I was hestitating to convert all the calls (they are many) to
> follow that improved paradigm.

Yes, leave that for another time.

     Andrew