From mboxrd@z Thu Jan 1 00:00:00 1970 X-GM-THRID: 6257896431456092160 X-Received: by 10.182.91.9 with SMTP id ca9mr4093054obb.7.1457054771871; Thu, 03 Mar 2016 17:26:11 -0800 (PST) X-BeenThere: outreachy-kernel@googlegroups.com Received: by 10.107.150.19 with SMTP id y19ls71372iod.105.gmail; Thu, 03 Mar 2016 17:26:11 -0800 (PST) X-Received: by 10.66.160.9 with SMTP id xg9mr4007594pab.38.1457054771372; Thu, 03 Mar 2016 17:26:11 -0800 (PST) Return-Path: Received: from mail-pf0-x22c.google.com (mail-pf0-x22c.google.com. [2607:f8b0:400e:c00::22c]) by gmr-mx.google.com with ESMTPS id y20si468913pfa.2.2016.03.03.17.26.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Mar 2016 17:26:11 -0800 (PST) Received-SPF: pass (google.com: domain of amsfield22@gmail.com designates 2607:f8b0:400e:c00::22c as permitted sender) client-ip=2607:f8b0:400e:c00::22c; Authentication-Results: gmr-mx.google.com; spf=pass (google.com: domain of amsfield22@gmail.com designates 2607:f8b0:400e:c00::22c as permitted sender) smtp.mailfrom=amsfield22@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.com Received: by mail-pf0-x22c.google.com with SMTP id 4so25162148pfd.1 for ; Thu, 03 Mar 2016 17:26:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:subject:date:message-id:in-reply-to:references; bh=u+ujKI0rMSKte4IsZNZQDy3fYsO8eoOI29/VGmOuORE=; b=ccmuKP9MI5EPqcm68aVzzjE/WxEbaUvMkZAVTO2fheHAt+gA8qsL/VCVTckTRkPiun y+qZv5RMY1ao30lJDXHATHuIrQCUt8wudmtV8iBj8i0cKbBMOH62D8VuCIHtXNr3M+Gq wwoaAfbFAXseCW9IWkh2dtBQTrX+W7FFaYFxdLbqoiI2HFJexsFPdyi+hkGwF8FCv9qk 9f8m+RMaY8jaRLhIji+CvEDy41Kki595/A4/YGwnrmXKU3hfl6ki5eWb2Yp0H+wy9Kw9 T3SvLNchpMMrMYnBM/f7Cgkp+/GSeXL5F2FXoQAgTJqRx+f+j5MJjnD4s9+/08rC9Mly lNZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:subject:date:message-id:in-reply-to :references; bh=u+ujKI0rMSKte4IsZNZQDy3fYsO8eoOI29/VGmOuORE=; b=bvNEZ/KgThx+04pFKUIZY6hQvB7lSAQQm12Fs0InlCoYmCG0A0e+n3pkD0XLG7VL88 WP1xAOslfr9pXKTGrnczQ9YE4PcZtJlFUKcF9oQQePrC81NY7B+3ZUQqXqxXb6R5xNNz zCqiD+DJhFl4LQ3vujhTYBMP96FcCnETjasCuepgd8M3GT+4lh3rAyFErntYRGa6GD67 rygi74CSU1QcUUgrgmpyxHPzGuM9OTqJRdqJIGYq2wB+kcX7N/8+HVyPlDvS38sPz/DY dLE+BDm3359hvff9SCF7ktySU15020lU3KFlGzG1GG+gbms9NAcM23UojN/mSbe5vgnv /5rg== X-Gm-Message-State: AD7BkJL2qIaXTAFOCl4sb8SodRljIDTt/9pyjNvY9uDZaKMzQObKkNW8NXElM7GawpxEbg== X-Received: by 10.98.16.70 with SMTP id y67mr8193310pfi.166.1457054771197; Thu, 03 Mar 2016 17:26:11 -0800 (PST) Return-Path: Received: from localhost.localdomain (or-67-232-68-68.dhcp.embarqhsd.net. [67.232.68.68]) by smtp.gmail.com with ESMTPSA id 9sm915437pft.44.2016.03.03.17.26.10 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 03 Mar 2016 17:26:10 -0800 (PST) From: Alison Schofield To: outreachy-kernel@googlegroups.com Subject: Re: [PATCH] Staging: fbtft: Do not use same argument more than once in bit operation. Date: Thu, 3 Mar 2016 17:26:02 -0800 Message-Id: <1457054762-3682-1-git-send-email-amsfield22@gmail.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: References: The reason may be that author is trying to to explicitly reflect the register settings. Considering this code... static int init_display(struct fbtft_par *par) { .................snip........................ /* Set temperature compensation */ write_reg(par, 0x24 | (temp & 0x03)); /* Set panel loading */ write_reg(par, 0x28 | (load & 0x03)); /* Set pump control */ write_reg(par, 0x2C | (pump & 0x03)); /* Set inverse display */ write_reg(par, 0xA6 | (0x01 & 0x01)); /* Set 4-bit grayscale mode */ write_reg(par, 0xD0 | (0x02 & 0x03)); In the first 3 commands temp,load,pump are vars &'d with a mask. In the last 2 commands 0x01 and 0x02 are hardcoded values &'d with a mask. Sometimes that hardcoded value just happens to be the same as its mask. I might even guess that this author knew it was redundant, but that the compiler would reduce all of that for him anyway. you can see the register definitions here if you want to get to very bottom of this ;) http://lcdhype.condense.de/index.php?act=Attach&type=post&id=6112&index=0 I wonder if it is better to define all those hardcode values for even more clarity.