On Wed, Jun 20, 2018 at 11:25:08AM -0700, 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.
>
I spent (wasted) some time browsing through the kernel.
Similar typecasts are only used if there is a real type change.
A warning here would not make sense unless NPCM7XX_FAN_TIEN_TAIEN
or NPCM7XX_FAN_TIEN_TEIEN would be outside the u8 range, and then
there would be one anyway.
So, no, I am not going to accept those typecasts. They just make the code
more difficult to read. For example, the code here could have been
simplified to something like
reg_int = ioread8(NPCM7XX_FAN_REG_TIEN(data->fan_base, fan));
reg_mode = ioread8(NPCM7XX_FAN_REG_TCKC(data->fan_base, fan));
if (cmp == NPCM7XX_FAN_CMPA) {
reg_int |= NPCM7XX_FAN_TIEN_TAIEN | NPCM7XX_FAN_TIEN_TEIEN;
reg_mode |= NPCM7XX_FAN_TCKC_CLK1_APB;
} else {
reg_int |= NPCM7XX_FAN_TIEN_TBIEN | NPCM7XX_FAN_TIEN_TFIEN;
reg_mode |= NPCM7XX_FAN_TCKC_CLK2_APB;
}
iowrite8(reg_int, NPCM7XX_FAN_REG_TIEN(data->fan_base, fan);
iowrite8(reg_mode, NPCM7XX_FAN_REG_TCKC(data->fan_base, fan);
This, in turn, leads to the question if it is really not necessary
to _clear_ those mask bits in the same context.
Guenter
> 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
>
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