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

From: Daniel Golle <daniel@makrotopia.org>
To: Andrew Lunn <andrew@lunn.ch>
Cc: netdev@vger.kernel.org, linux-mediatek@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	Sean Wang <sean.wang@mediatek.com>,
	Landen Chao <Landen.Chao@mediatek.com>,
	DENG Qingfang <dqfext@gmail.com>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Sam Shih <Sam.Shih@mediatek.com>,
	Lorenzo Bianconi <lorenzo@kernel.org>,
	John Crispin <john@phrozen.org>, Felix Fietkau <nbd@nbd.name>
Subject: Re: [RFC PATCH net-next v3 03/15] net: dsa: mt7530: use regmap to access switch register space
Date: Wed, 29 Mar 2023 19:33:17 +0100	[thread overview]
Message-ID: <ZCSEbUt9kj8Ta6Yc@makrotopia.org> (raw)
In-Reply-To: <7eb07ed2-2b1c-44fa-b029-0ecad7872fd2@lunn.ch>

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.
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.

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

Should I?