Re: fbdev: ssd1307fb: Unify init code and obtain hw specific bits from DT

["Thomas Niederprüm" <niederp@physik.uni-kl.de>]

Am Sat, 23 May 2015 20:32:45 +0300
schrieb Dan Carpenter <dan.carpenter@oracle.com>:

> Hello Thomas Niederprüm,
> 
> The patch a3998fe03e87: "fbdev: ssd1307fb: Unify init code and obtain
> hw specific bits from DT" from Mar 31, 2015, leads to the following
> static checker warning:
> 
> 	drivers/video/fbdev/ssd1307fb.c:371 ssd1307fb_init()
> 	warn: add some parenthesis here?
> 
> drivers/video/fbdev/ssd1307fb.c
>    366          /* Set COM pins configuration */
>    367          ret = ssd1307fb_write_cmd(par->client,
> SSD1307FB_SET_COM_PINS_CONFIG); 368          if (ret < 0)
>    369                  return ret;
>    370  
>    371          compins = 0x02 | (!par->com_seq & 0x1) << 4
>    372                                     | (par->com_lrremap & 0x1)
> << 5;
> 
> Smatch is complaining because it's normally  "!par->com_seq & 0x1" is
> a bug and "!(par->com_seq & 0x1)" is intended.  I don't know what was
> intended here though.  If the current code is correct, you can silence
> the static checker warning by writing it as "(!par->com_seq) & 0x1".

Indeed "!(par->com_seq & 0x1)" is what I intended. Thanks for spotting
this. 
What is the best way to handle this now? Will you send a fixup
patch as for the backlight code or will this be my task?

> 
> But I also have a hard time remembering if | or << is higher
> precedence so that might be clearer with parenthesis as well even
> though the code is clearly correct when I google for "order of
> operations" in C.
> 
>    373          ret = ssd1307fb_write_cmd(par->client, compins);
>    374          if (ret < 0)
>    375                  return ret;
> 

Thanks!

Thomas