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

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Message-ID: <20241028-great-worm-of-snow-494fa0-mkl@pengutronix.de>
Date: Mon, 28 Oct 2024 15:18:05 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Hal Feng <hal.feng@...rfivetech.com>
Cc: Andrew Lunn <andrew@...n.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	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" <devicetree@...r.kernel.org>, 
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
	"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: RE: [PATCH v2 3/4] can: Add driver for CAST CAN Bus Controller

On 23.09.2024 07:53:24, Hal Feng wrote:
> > > +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.
> 
> The hardware has been initially developed as peripheral component for 8 bit systems
> and therefore control and status registers defined as 8 bit groups. Nevertheless
> the hardware is designed as a 32 bit component finally. It prefers 32-bit read/write
> interfaces. I will add a comment later.

As mentioned in my v1 review, you are doing proper u32 accesses.

> > > +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?
> 
> Will use netdev_err() and return -EWOULDBLOCK instead.

You have a dedicated function to put the IP core into reset
"ccan_set_reset_mode()". If you don't trust you IP core or it needs some
time, add a poll to that function and return an error.

Then there's no need on ccan_bittime_configuration() to check for reset
mode.

Marc

-- 
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