linux-kernel - Re: [PATCH v2 3/4] can: Add driver for CAST CAN Bus Controller

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Message-ID: <cf17f15b-cbd7-4692-b3b2-065e549cb21e@lunn.ch>
Date: Sun, 22 Sep 2024 18:33:57 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Hal Feng <hal.feng@...rfivetech.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Vincent Mailhol <mailhol.vincent@...adoo.fr>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Emil Renner Berthing <emil.renner.berthing@...onical.com>,
	William Qiu <william.qiu@...rfivetech.com>,
	devicetree@...r.kernel.org, linux-can@...r.kernel.org,
	netdev@...r.kernel.org, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] can: Add driver for CAST CAN Bus Controller

> +static inline u32 ccan_read_reg(const struct ccan_priv *priv, u8 reg)
> +{
> +	return ioread32(priv->reg_base + reg);
> +}
> +
> +static inline void ccan_write_reg(const struct ccan_priv *priv, u8 reg, u32 value)
> +{
> +	iowrite32(value, priv->reg_base + reg);
> +}

No inline functions in .c files please. Let the compiler decide.

> +static inline u8 ccan_read_reg_8bit(const struct ccan_priv *priv,
> +				    enum ccan_reg reg)
> +{
> +	u8 reg_down;
> +	union val {
> +		u8 val_8[4];
> +		u32 val_32;
> +	} val;
> +
> +	reg_down = ALIGN_DOWN(reg, 4);
> +	val.val_32 = ccan_read_reg(priv, reg_down);
> +	return val.val_8[reg - reg_down];

There is an ioread8(). Is it invalid to do a byte read for this
hardware? If so, it is probably worth a comment.

> +static int ccan_bittime_configuration(struct net_device *ndev)
> +{
> +	struct ccan_priv *priv = netdev_priv(ndev);
> +	struct can_bittiming *bt = &priv->can.bittiming;
> +	struct can_bittiming *dbt = &priv->can.data_bittiming;
> +	u32 bittiming, data_bittiming;
> +	u8 reset_test;
> +
> +	reset_test = ccan_read_reg_8bit(priv, CCAN_CFG_STAT);
> +
> +	if (!(reset_test & CCAN_RST_MASK)) {
> +		netdev_alert(ndev, "Not in reset mode, cannot set bit timing\n");
> +		return -EPERM;
> +	}


You don't see nedev_alert() used very often. If this is fatal then
netdev_err().

Also, EPERM? man 3 errno say:

       EPERM           Operation not permitted (POSIX.1-2001).

Why is this a permission issue?

> +static void ccan_tx_interrupt(struct net_device *ndev, u8 isr)
> +{
> +	struct ccan_priv *priv = netdev_priv(ndev);
> +
> +	/* wait till transmission of the PTB or STB finished */
> +	while (isr & (CCAN_TPIF_MASK | CCAN_TSIF_MASK)) {
> +		if (isr & CCAN_TPIF_MASK)
> +			ccan_reg_set_bits(priv, CCAN_RTIF, CCAN_TPIF_MASK);
> +
> +		if (isr & CCAN_TSIF_MASK)
> +			ccan_reg_set_bits(priv, CCAN_RTIF, CCAN_TSIF_MASK);
> +
> +		isr = ccan_read_reg_8bit(priv, CCAN_RTIF);
> +	}

Potentially endless loops like this are a bad idea. If the firmware
crashes, you are never getting out of here. Please use one of the
macros from iopoll.h

> +static irqreturn_t ccan_interrupt(int irq, void *dev_id)
> +{
> +	struct net_device *ndev = (struct net_device *)dev_id;

dev_id is a void *, so you don't need the cast.

	Andrew