linux-kernel - Re: [PATCH] USB: remove redundant assignment to temp

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Date:   Tue, 7 Nov 2017 10:42:51 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Colin King <colin.king@...onical.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <kernel-janitors@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: remove redundant assignment to temp

On Tue, 7 Nov 2017, Colin King wrote:

> From: Colin Ian King <colin.king@...onical.com>
> 
> The variable temp is being set at the end of each loop iteration
> but this value is never read, it is either being updated in just
> the case 1 block or at the end of the loop.  Thus the assignment
> is redundant and can be removed.  Cleans up clang warning:
> 
> drivers/usb/host/ehci-dbg.c:840:4: warning: Value stored to 'temp'
> is never read
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/usb/host/ehci-dbg.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/usb/host/ehci-dbg.c b/drivers/usb/host/ehci-dbg.c
> index 7fb21d01b3d0..70d4768958be 100644
> --- a/drivers/usb/host/ehci-dbg.c
> +++ b/drivers/usb/host/ehci-dbg.c
> @@ -838,7 +838,6 @@ static ssize_t fill_registers_buffer(struct debug_buffer *buf)
>  			default:		/* unknown */
>  				break;
>  			}
> -			temp = (cap >> 8) & 0xff;
>  		}
>  	}
>  #endif

Good catch, but the solution is wrong.  The original code was mistaken;
it should have said:

			offset = (cap >> 8) & 0xff;

You can see that something like this is necessary if you consider the 
code path for the case where (cap & 0xff) != 1 -- the loop would just 
read the same capability value over and over again.

Would you like to submit a revised patch?

Alan Stern