Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751627AbbEBQhH (ORCPT ); Sat, 2 May 2015 12:37:07 -0400 Received: from mail-wg0-f51.google.com ([74.125.82.51]:32833 "EHLO mail-wg0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751114AbbEBQhD (ORCPT ); Sat, 2 May 2015 12:37:03 -0400 Date: Sat, 2 May 2015 17:36:59 +0100 From: Peter Griffin To: Thomas Gleixner Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, srinivas.kandagatla@gmail.com, maxime.coquelin@st.com, patrice.chotard@st.com, daniel.lezcano@linaro.org, lee.jones@linaro.org, devicetree@vger.kernel.org, Ajit Pal Singh Subject: Re: [PATCH 1/5] clocksource: st_lpc: Add LPC timer as a clocksource. Message-ID: <20150502163659.GA23998@griffinp-ThinkPad-X1-Carbon-2nd> References: <1429267823-8879-1-git-send-email-peter.griffin@linaro.org> <1429267823-8879-2-git-send-email-peter.griffin@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 2002 Lines: 64 Hi Thomas, On Tue, 21 Apr 2015, Thomas Gleixner wrote: > On Fri, 17 Apr 2015, Peter Griffin wrote: > > +/* Low Power Timer */ > > +#define LPC_LPT_LSB_OFF 0x400 > > +#define LPC_LPT_MSB_OFF 0x404 > > +#define LPC_LPT_START_OFF 0x408 > > + > > +struct st_lpc { > > + struct clk *clk; > > + void __iomem *iomem_cs; > > +}; > > + > > +static struct st_lpc *st_lpc; > > + > > +static u64 notrace st_lpc_counter_read(void) > > +{ > > + u64 counter; > > + u32 lower; > > + u32 upper, old_upper; > > + > > + upper = readl_relaxed(st_lpc->iomem_cs + LPC_LPT_MSB_OFF); > > + do { > > + old_upper = upper; > > + lower = readl_relaxed(st_lpc->iomem_cs + LPC_LPT_LSB_OFF); > > + upper = readl_relaxed(st_lpc->iomem_cs + LPC_LPT_MSB_OFF); > > + } while (upper != old_upper); > > + > > + counter = upper; > > + counter <<= 32; > > + counter |= lower; > > + return counter; > > > What's the point of this exercise? The kernel can handle 32bit > clocksources nicely. So why do you want to artificially expand them to > 64bit by adding useless loops and hoops to a hotpath? Thanks for reviewing, yes your correct, we don't really need to be doing this. We will fix this in the v2 version. Lee Jones has also pointed out something which I was not aware of when submitting this, and that is this IP has shared registers with the RTC driver. He has been working on some patches here https://lkml.org/lkml/2015/4/9/609 which deal with configuring between watchdog and rtc and ensuring only one can be configured at a time, and this driver should also be making use of that mechanism. As he is already working on this, we decided it would be best if he takes over for the V2 submission, and aligns it with the work he has already done for this IP. regards, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/