linux-kernel - Re: [PATCH] usb: usb251xb: Remove unnecessary comparison of unsigned integer with >= 0

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Date:   Mon, 18 Mar 2019 17:48:11 +0100
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Richard Leitner <richard.leitner@...data.com>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: usb251xb: Remove unnecessary comparison of unsigned
 integer with >= 0

Hi Richard,

On 19-03-18 16:46, Richard Leitner wrote:
> Hi Marco, Hi Gustavo,
> thanks for the fix, please feel free to add
> 
> 	Reviewed-by: Richard Leitner <richard.leitner@...data.com>
> 
> On 18/03/2019 16:34, Marco Felsch wrote:
> > Hi Silva,
> > 
> > On 19-03-18 09:50, Gustavo A. R. Silva wrote:
> > > There is no need to compare *port* with >= 0 because such comparison
> > > of an unsigned value is always true.
> > 
> > Absolutly.. It seems that it was an copy'n'paste failure. Thanks for
> > fixing that.
> 
> A small note on further improvement from my side:
> 
> According the datasheet, when you set swap-dx-lanes to 0 (-> setting port to
> 0 -> setting bit 0 of PRTSP) "   the upstream port DP/DM is swapped".

Yes I know that's not intuitve and may confuses the users.

> IMHO this is not straight-forward, so maybe we want to additionally
> 
> 	a) mention it somewhere in the documentation

IMHO this is the correct place.

> 	b) check on port >= 1

I think this isn't doable since we shouldn't break the existing dt.

Regards,
Marco

> 	c) something else?
> 
> Any opinions on that from your side? ... I'd prefer "a"...
> 
> regards;Richard.L
> 
> > 
> > Regards,
> > Marco
> > 
> > > Fix this by removing such comparison.
> > > 
> > > Addresses-Coverity-ID: 1443949 ("Unsigned compared against 0")
> > > Fixes: 02a50b875046 ("usb: usb251xb: add usb data lane port swap feature")
> > > Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> > > ---
> > >   drivers/usb/misc/usb251xb.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c
> > > index 4d72b7d1d383..2c8e2cad7e10 100644
> > > --- a/drivers/usb/misc/usb251xb.c
> > > +++ b/drivers/usb/misc/usb251xb.c
> > > @@ -547,7 +547,7 @@ static int usb251xb_get_ofdata(struct usb251xb *hub,
> > >   	 */
> > >   	hub->port_swap = USB251XB_DEF_PORT_SWAP;
> > >   	of_property_for_each_u32(np, "swap-dx-lanes", prop, p, port) {
> > > -		if ((port >= 0) && (port <= data->port_cnt))
> > > +		if (port <= data->port_cnt)
> > >   			hub->port_swap |= BIT(port);
> > >   	}
> > > -- 
> > > 2.21.0
> > > 
> > > 
> > 
> 

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