linux-kernel - Re: [PATCH v2 2/2] hwmon: npcm750: add NPCM7xx PWM and Fan driver

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Date:   Wed, 20 Jun 2018 11:25:08 -0700
From:   Joe Perches <joe@...ches.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Tomer Maimon <tmaimon77@...il.com>,
        Julia Lawall <julia.lawall@...6.fr>,
        cocci <cocci@...teme.lip6.fr>
Cc:     robh+dt@...nel.org, mark.rutland@....com, jdelvare@...e.com,
        avifishman70@...il.com, yuenn@...gle.com,
        brendanhiggins@...gle.com, venture@...gle.com, joel@....id.au,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hwmon@...r.kernel.org, openbmc@...ts.ozlabs.org
Subject: Re: [PATCH v2 2/2] hwmon: npcm750: add NPCM7xx PWM and Fan driver

(adding Julia Lawall and cocci mailing list)

On Wed, 2018-06-20 at 09:48 -0700, Guenter Roeck wrote:
[]
> > +static inline void npcm7xx_fan_start_capture(struct npcm7xx_pwm_fan_data *data,
> > +						 u8 fan, u8 cmp)
> > +{
> > +	u8 fan_id = 0;
> > +	u8 reg_mode = 0;
> > +	u8 reg_int = 0;
> > +	unsigned long flags;
> > +
> > +	fan_id = NPCM7XX_FAN_INPUT(fan, cmp);
> > +
> > +	/* to check whether any fan tach is enable */
> > +	if (data->npcm7xx_fan[fan_id].FanStFlag != FAN_DISABLE) {
> > +		/* reset status */
> > +		spin_lock_irqsave(&data->npcm7xx_fan_lock[fan], flags);
> > +
> > +		data->npcm7xx_fan[fan_id].FanStFlag = FAN_INIT;
> > +		reg_int = ioread8(NPCM7XX_FAN_REG_TIEN(data->fan_base, fan));
> > +
> > +		if (cmp == NPCM7XX_FAN_CMPA) {
> > +			/* enable interrupt */
> > +			iowrite8((u8) (reg_int | (NPCM7XX_FAN_TIEN_TAIEN |
> > +						  NPCM7XX_FAN_TIEN_TEIEN)),
> 
> Is the (u8) typecast really necessary ? Seems unlikely.

The cast is not really necessary here as there would
be an implicit cast already.

Some might complain about loss of type safety and
"make W=123" would probably emit something here.

But casts to the same type are not necessary.

A possible coccinelle script to find casts to the
same type is below, but there are some false positives
for things like __force and __user casts

Also, spatch (1.0.4) seems to have a defect for this
when the type is used in operations that change a
smaller type to int or unsigned int.

i.e.: (offset is u16, but offset * 2 is int)

While running the cocci script below:

HANDLING: drivers/net/ethernet/intel/igb/e1000_nvm.c
diff = 
diff -u -p a/drivers/net/drivers/net/ethernet/intel/igb/e1000_nvm.c b/drivers/net/ethernet/intel/igb/e1000_nvm.c
--- a/drivers/net/ethernet/intel/igb/e1000_nvm.c
+++ b/drivers/net/ethernet/intel/igb/e1000_nvm.c
@@ -335,7 +335,7 @@ s32 igb_read_nvm_spi(struct e1000_hw *hw
 
 	/* Send the READ command (opcode + addr) */
 	igb_shift_out_eec_bits(hw, read_opcode, nvm->opcode_bits);
-	igb_shift_out_eec_bits(hw, (u16)(offset*2), nvm->address_bits);
+	igb_shift_out_eec_bits(hw, (offset * 2), nvm->address_bits);
 
 	/* Read the data.  SPI NVMs increment the address with each byte
 	 * read and will roll over if reading beyond the end.  This allows

---

Anyway, here's the cocci script:

$ cat same_typecast.cocci
@@
type T;
T foo;
@@

-	(T *)&foo
+	&foo

@@
type T;
T foo;
@@

-	(T)foo
+	foo