linux-kernel - Re: [PATCH] net: can: cc770: Simplify parsing DT properties

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Message-ID: <20240829-spiked-amigurumi-bloodhound-d94a6c-mkl@pengutronix.de>
Date: Thu, 29 Aug 2024 21:35:39 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Simon Horman <horms@...nel.org>
Cc: "Rob Herring (Arm)" <robh@...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>, linux-can@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: can: cc770: Simplify parsing DT properties

On 28.08.2024 17:16:24, Simon Horman wrote:
> On Wed, Aug 28, 2024 at 08:19:02AM -0500, Rob Herring (Arm) wrote:
> > Use of the typed property accessors is preferred over of_get_property().
> > The existing code doesn't work on little endian systems either. Replace
> > the of_get_property() calls with of_property_read_bool() and
> > of_property_read_u32().
> > 
> > Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> 
> ...
> 
> > diff --git a/drivers/net/can/cc770/cc770_platform.c b/drivers/net/can/cc770/cc770_platform.c
> > index 13bcfba05f18..9993568154f8 100644
> > --- a/drivers/net/can/cc770/cc770_platform.c
> > +++ b/drivers/net/can/cc770/cc770_platform.c
> > @@ -71,16 +71,9 @@ static int cc770_get_of_node_data(struct platform_device *pdev,
> >  				  struct cc770_priv *priv)
> >  {
> >  	struct device_node *np = pdev->dev.of_node;
> > -	const u32 *prop;
> > -	int prop_size;
> > -	u32 clkext;
> > -
> > -	prop = of_get_property(np, "bosch,external-clock-frequency",
> > -			       &prop_size);
> > -	if (prop && (prop_size ==  sizeof(u32)))
> > -		clkext = *prop;
> > -	else
> > -		clkext = CC770_PLATFORM_CAN_CLOCK; /* default */
> > +	u32 clkext = CC770_PLATFORM_CAN_CLOCK, clkout = 0;
> 
> Marc,
> 
> Could you clarify if reverse xmas tree ordering - longest line to shortest
> - of local variables is desired for can code? If so, I'm flagging that the
> above now doesn't follow that scheme.

If you touch the code, and noting speaks against it, please make it
reverse xmas.

> 
> > +
> > +	of_property_read_u32(np, "bosch,external-clock-frequency", &clkext);
> >  	priv->can.clock.freq = clkext;
> >  
> >  	/* The system clock may not exceed 10 MHz */
> 
> ...
> 
> > @@ -109,20 +102,16 @@ static int cc770_get_of_node_data(struct platform_device *pdev,
> >  	if (of_property_read_bool(np, "bosch,polarity-dominant"))
> >  		priv->bus_config |= BUSCFG_POL;
> >  
> > -	prop = of_get_property(np, "bosch,clock-out-frequency", &prop_size);
> > -	if (prop && (prop_size == sizeof(u32)) && *prop > 0) {
> > -		u32 cdv = clkext / *prop;
> > -		int slew;
> > +	of_property_read_u32(np, "bosch,clock-out-frequency", &clkout);
> > +	if (clkout > 0) {
> > +		u32 cdv = clkext / clkout;
> > +		u32 slew;
> >  
> >  		if (cdv > 0 && cdv < 16) {
> >  			priv->cpu_interface |= CPUIF_CEN;
> >  			priv->clkout |= (cdv - 1) & CLKOUT_CD_MASK;
> >  
> > -			prop = of_get_property(np, "bosch,slew-rate",
> > -					       &prop_size);
> > -			if (prop && (prop_size == sizeof(u32))) {
> > -				slew = *prop;
> > -			} else {
> > +			if (of_property_read_u32(np, "bosch,slew-rate", &slew)) {
> >  				/* Determine default slew rate */
> >  				slew = (CLKOUT_SL_MASK >>
> >  					CLKOUT_SL_SHIFT) -
> 
> Rob,
> 
> The next few lines look like this:
> 
> 					((cdv * clkext - 1) / 8000000);
> 				if (slew < 0)
> 					slew = 0;
> 
> But slew is now unsigned, so this check will always be false.
> 
> Flagged by Smatch and Coccinelle.

Good finding.

Thanks,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
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