linux-kernel - Re: [PATCH][next] tty: serial: jsm: remove redundant assignments of several variables

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Date:   Thu, 22 Apr 2021 15:15:18 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Lee Jones <lee.jones@...aro.org>, linux-serial@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] tty: serial: jsm: remove redundant assignments of
 several variables

On Thu, Apr 22, 2021 at 02:01:36PM +0100, Colin Ian King wrote:
> On 22/04/2021 13:56, Johan Hovold wrote:
> > On Thu, Apr 22, 2021 at 01:53:03PM +0100, Colin Ian King wrote:
> >> On 22/04/2021 13:52, Johan Hovold wrote:
> >>> On Thu, Apr 22, 2021 at 01:11:15PM +0100, Colin King wrote:
> >>>> From: Colin Ian King <colin.king@...onical.com>
> >>>>
> >>>> Several variables are being assigned with values that are never
> >>>> read and being updated later with a new value. The initializations
> >>>> are redundant and can be removed.
> >>>>
> >>>> Addresses-Coverity: ("Unused value")
> >>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> >>>> ---
> >>>>  drivers/tty/serial/jsm/jsm_cls.c | 6 ++----
> >>>>  1 file changed, 2 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/drivers/tty/serial/jsm/jsm_cls.c b/drivers/tty/serial/jsm/jsm_cls.c
> >>>> index b507a2cec926..b58ea4344aaf 100644
> >>>> --- a/drivers/tty/serial/jsm/jsm_cls.c
> >>>> +++ b/drivers/tty/serial/jsm/jsm_cls.c
> >>>> @@ -349,8 +349,8 @@ static void cls_assert_modem_signals(struct jsm_channel *ch)
> >>>>  
> >>>>  static void cls_copy_data_from_uart_to_queue(struct jsm_channel *ch)
> >>>>  {
> >>>> -	int qleft = 0;
> >>>> -	u8 linestatus = 0;
> >>>> +	int qleft;
> >>>> +	u8 linestatus;
> >>>>  	u8 error_mask = 0;
> >>>>  	u16 head;
> >>>>  	u16 tail;
> >>>> @@ -365,8 +365,6 @@ static void cls_copy_data_from_uart_to_queue(struct jsm_channel *ch)
> >>>>  	head = ch->ch_r_head & RQUEUEMASK;
> >>>>  	tail = ch->ch_r_tail & RQUEUEMASK;
> >>>>  
> >>>> -	/* Get our cached LSR */
> >>>> -	linestatus = ch->ch_cached_lsr;
> >>>>  	ch->ch_cached_lsr = 0;
> >>>
> >>> Why leave this assignment in? Looks like this was all copy-pasta, but
> >>> this assignment makes even less sense now that you remove the comment
> >>> and load.
> >>
> >> Which assignment are you referring to?
> > 
> > The one just above my comment: 
> > 
> > 	ch->ch_cached_lsr = 0;
> 
> that cached value is being used in jsm_neo.c, so removing the zero'ing
> may cause some issues.

That's for you to determine, right? Only doing half of a clean may
actually be worse than doing nothing at all. At least now it's somewhat
clear why that statement is there.

The jsm_neo.c implements support for a different class of devices and
only those actually use ch_cached_lsr AFAICT.

It would be good if you include some context in the commit message such
as which commit added this code and that it has never been used.

Johan