Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422697AbbD2JtS (ORCPT ); Wed, 29 Apr 2015 05:49:18 -0400 Received: from mail-vn0-f44.google.com ([209.85.216.44]:35752 "EHLO mail-vn0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966091AbbD2JtM convert rfc822-to-8bit (ORCPT ); Wed, 29 Apr 2015 05:49:12 -0400 MIME-Version: 1.0 In-Reply-To: <11982715D62E664DBACA4351A418B0581437DA7C@IRSMSX107.ger.corp.intel.com> References: <1429862240-21619-1-git-send-email-anda-maria.nicolae@intel.com> <11982715D62E664DBACA4351A418B0581437DA51@IRSMSX107.ger.corp.intel.com> <11982715D62E664DBACA4351A418B0581437DA7C@IRSMSX107.ger.corp.intel.com> Date: Wed, 29 Apr 2015 18:49:11 +0900 Message-ID: Subject: Re: [PATCH] power_supply: Add support for Richtek rt9455 battery charger From: =?UTF-8?Q?Krzysztof_Koz=C5=82owski?= To: "Nicolae, Anda-maria" Cc: "sre@kernel.org" , "dbaryshkov@gmail.com" , "robh+dt@kernel.org" , "pawel.moll@arm.com" , "mark.rutland@arm.com" , "ijc+devicetree@hellion.org.uk" , "galak@codeaurora.org" , "dwmw2@infradead.org" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3578 Lines: 65 2015-04-27 23:02 GMT+09:00 Nicolae, Anda-maria : > However after looking at the code I got different question. You are > reading here and in few other places the RT9455_REG_IRQ1. Isn't the > register auto-cleared? > > No, RT9455_REG_IRQ1 is not cleared after reading. Let me give you an example. Suppose the battery is missing, so BATAB bit is set. This bit remains set until the battery is reconnected to the charger, independent of the number of i2c_reads over RT9455_REG_IRQ1. Unfortunately, no interrupt is triggered when the battery is reconnected (and BATAB bit is cleared). OK, I got it. > > (...) > >>> + >>> +#if IS_ENABLED(CONFIG_USB_PHY) >>> + info->usb_phy = usb_get_phy(USB_PHY_TYPE_USB2); >>> + if (IS_ERR_OR_NULL(info->usb_phy)) { >>> + dev_err(dev, "Failed to get USB transceiver\n"); >>> + } else { >>> + info->nb.notifier_call = rt9455_usb_event; >>> + ret = usb_register_notifier(info->usb_phy, &info->nb); >>> + if (ret) { >>> + dev_err(dev, "Failed to register USB notifier\n"); >>> + usb_put_phy(info->usb_phy); >>> + } >>> + } >>> +#endif >>> + >>> + INIT_DELAYED_WORK(&info->pwr_rdy_work, rt9455_pwr_rdy_work_callback); >>> + INIT_DELAYED_WORK(&info->max_charging_time_work, >>> + rt9455_max_charging_time_work_callback); >>> + INIT_DELAYED_WORK(&info->batt_presence_work, >>> + rt9455_batt_presence_work_callback); >> >> Maybe any of these could be made as DEFERRABLE_WORK? Just thinking out loud... >> >> I cannot use DEFERRABLE_WORK instead of DELAYED_WORK. DEFERRABLE_WORK runs in interrupt context, while DELAYED_WORK runs in process context. All handlers for DELAYED_WORK from the driver perform read/write operations via I2C, which may sleep. This is the reason why DELAYED_WORK is used. > > AFAIK, the context is the same. The only difference is the type of > timer used for scheduling the work. In case of deferrable timer it > won't wake up a sleeping CPU. Which means that it may be executed some > unspecified time in the future. This has energy conserving benefits > but may not be appropriate for your case because you could want to > poll the battery status in exact intervals. > > Just to understand correctly, you mean that if I use DEFERRABLE_WORK, I will not get kernel panic with message "scheduling while atomic"? This is what happens if I use timers and I thought that I would get the same result with DEFERRABLE_WORK. Actually, the timers are not critical and status of the charger may be checked some fraction of a second later. You shouldn't get that panic. Deferrable work is used in few other similar places. As you can check in the include/linux/workqueue.h file the timers are used in both cases. The INIT_DELAYED_WORK already uses a flag for timers - TIMER_IRQSAFE. However for deferrable work it uses additional flag - deferrable timer. Unfortunately the difference may not be a "fraction of a second later". Actually the difference may be as much as 1 second later for the fully non-tickless system. If system is truly idle, the deferrable timers (and work) may not fire for long time. So this must be considered. Best regards, Krzysztof -- 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/