On Tue, 5 Sep 2017, Arnd Bergmann wrote:
> gcc-8 points out two comparisons that are clearly bogus
> and almost certainly not what the author intended to write:
>
> drivers/usb/gadget/udc/dummy_hcd.c: In function 'set_link_state_by_speed':
> drivers/usb/gadget/udc/dummy_hcd.c:379:31: error: bitwise comparison always
> evaluates to false [-Werror=tautological-compare]
> USB_PORT_STAT_ENABLE) == 1 &&
> ^~
> drivers/usb/gadget/udc/dummy_hcd.c:381:25: error: bitwise comparison always
> evaluates to false [-Werror=tautological-compare]
> USB_SS_PORT_LS_U0) == 1 &&
> ^~
>
> I looked at the code for a bit and came up with a change that makes
> it look like what the author probably meant here. This makes it
> look reasonable to me and to gcc, shutting up the warning.
>
> It does of course change behavior as the two conditions are actually
> evaluated rather than being hardcoded to false, and I have made no
> attempt at verifying that the changed logic makes sense in the context
> of a USB HCD, so that part needs to be reviewed carefully.
>
> Fixes: 1cd8fd2887e1 ("usb: gadget: dummy_hcd: add SuperSpeed support")
> Cc: Tatyana Brokhman <tlin...@codeaurora.org>
> Cc: Felipe Balbi <ba...@ti.com>
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
> drivers/usb/gadget/udc/dummy_hcd.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/dummy_hcd.c
> b/drivers/usb/gadget/udc/dummy_hcd.c
> index a030d7923d7d..54e8e37d2bc8 100644
> --- a/drivers/usb/gadget/udc/dummy_hcd.c
> +++ b/drivers/usb/gadget/udc/dummy_hcd.c
> @@ -376,10 +376,10 @@ static void set_link_state_by_speed(struct dummy_hcd
> *dum_hcd)
> dum_hcd->port_status |=
> (USB_PORT_STAT_C_CONNECTION << 16);
> if ((dum_hcd->port_status &
> - USB_PORT_STAT_ENABLE) == 1 &&
> - (dum_hcd->port_status &
> - USB_SS_PORT_LS_U0) == 1 &&
> - dum_hcd->rh_state != DUMMY_RH_SUSPENDED)
> + USB_PORT_STAT_ENABLE) == USB_PORT_STAT_ENABLE &&
This test can simply become (dum_hcd->port_status & USB_PORT_STAT_ENABLE),
since the latter is a single bit. If you don't mind making its form
different from the forms of the other two tests.
Alan Stern
> + (dum_hcd->port_status &
> + USB_PORT_STAT_LINK_STATE) == USB_SS_PORT_LS_U0 &&
> + dum_hcd->rh_state != DUMMY_RH_SUSPENDED)
> dum_hcd->active = 1;
> }
> } else {
>
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