From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757866AbbGGX02 (ORCPT ); Tue, 7 Jul 2015 19:26:28 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:57670 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757278AbbGGX0U (ORCPT ); Tue, 7 Jul 2015 19:26:20 -0400 Date: Tue, 7 Jul 2015 16:26:18 -0700 From: Stephen Boyd To: Andy Shevchenko Cc: linux-kernel@vger.kernel.org, Sascha Hauer , Peter De Schrijver , Tero Kristo , Russell King , Dinh Nguyen Subject: Re: [PATCH v3 1/7] clk: introduce clk_div_mask() helper Message-ID: <20150707232618.GE30412@codeaurora.org> References: <1427822547-163289-1-git-send-email-andriy.shevchenko@linux.intel.com> <1427822547-163289-2-git-send-email-andriy.shevchenko@linux.intel.com> <20150618194815.GK29640@codeaurora.org> <1436284082.10819.56.camel@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1436284082.10819.56.camel@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/07, Andy Shevchenko wrote: > On Thu, 2015-06-18 at 12:48 -0700, Stephen Boyd wrote: > > On 03/31, Andy Shevchenko wrote: > > > diff --git a/include/linux/clk-provider.h b/include/linux/clk > > > -provider.h > > > index 5591ea7..20b0b67 100644 > > > --- a/include/linux/clk-provider.h > > > +++ b/include/linux/clk-provider.h > > > @@ -353,6 +353,11 @@ struct clk_divider { > > > spinlock_t *lock; > > > }; > > > > > > +static inline unsigned long clk_div_mask(u8 width) > > > +{ > > > + return (1 << width) - 1; > > > +} > > > + > > > > Why not just change drivers to use GENMASK? It's a proven and > > tested way to generate a bitmask. > > Too many unneeded calculations I suppose. That's what compiler optimizations are for. > > Compare: > mask = clk_div_mask(mm) << ms; > which is simple ((1 << mm) - 1) << ms > and > mask = GENMASK(mm + ms - 1, ms); > which is (~0 << ms) & (~0 >> (BITS_PER_LONG - 1 - (mm + ms - > 1))) And if mm is 32 then we hit undefined behavior. > > > > > So I'd rather see drivers converted to use that macro directly > > especially because the mask may need to start at some bit that > > isn't 0. > > If you think the above is not a burden, I can do the conversion to > GENMASK. > > Though it might make sense when ms = 0 explicitly. > Yes let's use GENMASK. I imagine the extra few instructions are negligible. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project