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

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Message-ID: <alpine.DEB.2.20.1806211515060.3774@hadrien>
Date:   Thu, 21 Jun 2018 15:17:26 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Joe Perches <joe@...ches.com>
cc:     Guenter Roeck <linux@...ck-us.net>,
        Tomer Maimon <tmaimon77@...il.com>,
        cocci <cocci@...teme.lip6.fr>, 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



On Wed, 20 Jun 2018, Joe Perches wrote:

> (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)

Ah.  The rule is that the result type is always the larger one?
Unfortunately, Coccinelle doesn't know the size of any type.  I could add
some special cases, but that may be more confusing than helpful.

julia

>
> 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
>
>