From: Nathan Chancellor
> Sent: 14 October 2021 22:57
>
> A new warning in clang points out a place in this file where a bitwise
> OR is being used with boolean expressions:
>
> In file included from drivers/staging/wlan-ng/prism2usb.c:2:
> drivers/staging/wlan-ng/hfa384x_usb.c:3787:7: warning: use of bitwise '|' with boolean operands [-
> Wbitwise-instead-of-logical]
> ((test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
> ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/staging/wlan-ng/hfa384x_usb.c:3787:7: note: cast one or both operands to int to silence this
> warning
> 1 warning generated.
>
> The comment explains that short circuiting here is undesirable, as the
> calls to test_and_{clear,set}_bit() need to happen for both sides of the
> expression.
>
> Clang's suggestion would work to silence the warning but the readability
> of the expression would suffer even more. To clean up the warning and
> make the block more readable, use a variable for each side of the
> bitwise expression.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1478
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> drivers/staging/wlan-ng/hfa384x_usb.c | 22 +++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/staging/wlan-ng/hfa384x_usb.c b/drivers/staging/wlan-ng/hfa384x_usb.c
> index 59aa84d1837d..938e11a1a0b6 100644
> --- a/drivers/staging/wlan-ng/hfa384x_usb.c
> +++ b/drivers/staging/wlan-ng/hfa384x_usb.c
> @@ -3778,18 +3778,18 @@ static void hfa384x_usb_throttlefn(struct timer_list *t)
>
> spin_lock_irqsave(&hw->ctlxq.lock, flags);
>
> - /*
> - * We need to check BOTH the RX and the TX throttle controls,
> - * so we use the bitwise OR instead of the logical OR.
> - */
> pr_debug("flags=0x%lx\n", hw->usb_flags);
> - if (!hw->wlandev->hwremoved &&
> - ((test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
> - !test_and_set_bit(WORK_RX_RESUME, &hw->usb_flags)) |
> - (test_and_clear_bit(THROTTLE_TX, &hw->usb_flags) &&
> - !test_and_set_bit(WORK_TX_RESUME, &hw->usb_flags))
> - )) {
> - schedule_work(&hw->usb_work);
> + if (!hw->wlandev->hwremoved) {
> + bool rx_throttle = test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
> + !test_and_set_bit(WORK_RX_RESUME, &hw->usb_flags);
> + bool tx_throttle = test_and_clear_bit(THROTTLE_TX, &hw->usb_flags) &&
> + !test_and_set_bit(WORK_TX_RESUME, &hw->usb_flags);
> + /*
> + * We need to check BOTH the RX and the TX throttle controls,
> + * so we use the bitwise OR instead of the logical OR.
> + */
> + if (rx_throttle | tx_throttle)
> + schedule_work(&hw->usb_work);
Why not the slightly simpler:
bool throttle = test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
!test_and_set_bit(WORK_RX_RESUME, &hw->usb_flags);
throttle |= test_and_clear_bit(THROTTLE_TX, &hw->usb_flags) &&
!test_and_set_bit(WORK_TX_RESUME, &hw->usb_flags);
if (throttle)
schedule_work(&hw->usb_work);
or with s/throttle/throttle_silly_compiler_warning/ :-)
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
