Subject: Re: [PATCH] net: can: cc770: Simplify parsing DT properties

From: Simon Horman <[email-masked]>
Date: Wed, 28 Aug 2024 17:16:24 +0100

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) <[email-masked]>

...

> 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.

> +
> +	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.