From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D002C433F5 for ; Tue, 19 Apr 2022 19:36:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355816AbiDSTiw (ORCPT ); Tue, 19 Apr 2022 15:38:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54432 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355423AbiDSTiw (ORCPT ); Tue, 19 Apr 2022 15:38:52 -0400 Received: from relay6-d.mail.gandi.net (relay6-d.mail.gandi.net [IPv6:2001:4b98:dc4:8::226]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83D5641333; Tue, 19 Apr 2022 12:35:38 -0700 (PDT) Received: (Authenticated sender: alexandre.belloni@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id 7D8B0C0003; Tue, 19 Apr 2022 19:35:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1650396937; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NjVLNhCR4Pir1ny3Pd2NCoy9GPJ41cfM4aaT+ckLEEM=; b=WmUJdcNl52VVlvUpV8NVEAtr+PdL0pMSHN1QYoAf3T52RHemqet43OLCrmbAaAaeWwRoKl /FnURKNMomdhx6mbf9O4Ua4UJ1BwAErqYFeZvOf1CcsAsSe3O69wYMt4OgGLv13bVFgMDK 6RArYxInIs/b6+CjN9yi6B7TyUsFRG7DgzjABO0soPOvYmlQwH/GWc8vRO79vU4oUe+R4U ntqXlNBS9y9HcRyi7KGOP4jA+kKxo7dmGZYoZ3RE2KSaLVjMOnmadNtfm3wRdDXPj5B2Fn 3SKI6osT/stQLrNtQjqmHZX8dUyJXolJiJgX4vAnaeFCDGUowSW/4ih1d1E8Ow== Date: Tue, 19 Apr 2022 21:35:35 +0200 From: Alexandre Belloni To: Paul Cercueil Cc: Alessandro Zummo , list@opendingux.net, linux-rtc@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org Subject: Re: [PATCH 3/5] rtc: jz4740: Reset scratchpad register on power loss Message-ID: References: <20220418184933.13172-1-paul@crapouillou.net> <20220418184933.13172-4-paul@crapouillou.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220418184933.13172-4-paul@crapouillou.net> Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 18/04/2022 19:49:31+0100, Paul Cercueil wrote: > On power loss, reading the RTC value would fail as the scratchpad lost > its magic value, until the hardware clock was set once again. > > To avoid that, reset the RTC value to Epoch in the probe if we detect > that the scratchpad lost its magic value. > > Signed-off-by: Paul Cercueil > --- > drivers/rtc/rtc-jz4740.c | 24 +++++++++++++++++++++--- > 1 file changed, 21 insertions(+), 3 deletions(-) > > diff --git a/drivers/rtc/rtc-jz4740.c b/drivers/rtc/rtc-jz4740.c > index 119baf168b32..aac5f68bf626 100644 > --- a/drivers/rtc/rtc-jz4740.c > +++ b/drivers/rtc/rtc-jz4740.c > @@ -42,6 +42,9 @@ > /* Magic value to enable writes on jz4780 */ > #define JZ_RTC_WENR_MAGIC 0xA55A > > +/* Value written to the scratchpad to detect power losses */ > +#define JZ_RTC_SCRATCHPAD_MAGIC 0x12345678 > + > #define JZ_RTC_WAKEUP_FILTER_MASK 0x0000FFE0 > #define JZ_RTC_RESET_COUNTER_MASK 0x00000FE0 > > @@ -134,10 +137,11 @@ static int jz4740_rtc_ctrl_set_bits(struct jz4740_rtc *rtc, uint32_t mask, > static int jz4740_rtc_read_time(struct device *dev, struct rtc_time *time) > { > struct jz4740_rtc *rtc = dev_get_drvdata(dev); > - uint32_t secs, secs2; > + uint32_t secs, secs2, magic; > int timeout = 5; > > - if (jz4740_rtc_reg_read(rtc, JZ_REG_RTC_SCRATCHPAD) != 0x12345678) > + magic = jz4740_rtc_reg_read(rtc, JZ_REG_RTC_SCRATCHPAD); > + if (magic != JZ_RTC_SCRATCHPAD_MAGIC) > return -EINVAL; > > /* If the seconds register is read while it is updated, it can contain a > @@ -169,7 +173,8 @@ static int jz4740_rtc_set_time(struct device *dev, struct rtc_time *time) > if (ret) > return ret; > > - return jz4740_rtc_reg_write(rtc, JZ_REG_RTC_SCRATCHPAD, 0x12345678); > + return jz4740_rtc_reg_write(rtc, JZ_REG_RTC_SCRATCHPAD, > + JZ_RTC_SCRATCHPAD_MAGIC); > } > > static int jz4740_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm) > @@ -307,6 +312,7 @@ static int jz4740_rtc_probe(struct platform_device *pdev) > struct jz4740_rtc *rtc; > unsigned long rate; > struct clk *clk; > + uint32_t magic; > int ret, irq; > > rtc = devm_kzalloc(dev, sizeof(*rtc), GFP_KERNEL); > @@ -369,6 +375,18 @@ static int jz4740_rtc_probe(struct platform_device *pdev) > /* Each 1 Hz pulse should happen after (rate) ticks */ > jz4740_rtc_reg_write(rtc, JZ_REG_RTC_REGULATOR, rate - 1); > > + magic = jz4740_rtc_reg_read(rtc, JZ_REG_RTC_SCRATCHPAD); > + if (magic != JZ_RTC_SCRATCHPAD_MAGIC) { > + /* > + * If the scratchpad doesn't hold our magic value, then a > + * power loss occurred. Reset to Epoch. > + */ > + struct rtc_time time; > + > + rtc_time64_to_tm(0, &time); > + jz4740_rtc_set_time(dev, &time); Don't do that, this defeats the purpose of detecting when the power is lost. Returning a known bogus time is the worst thing you can do here. > + } > + > ret = devm_rtc_register_device(rtc->rtc); > if (ret) > return ret; > -- > 2.35.1 > -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com