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 A5BA9C7EE2E for ; Sat, 10 Jun 2023 08:31:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231132AbjFJIbn (ORCPT ); Sat, 10 Jun 2023 04:31:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229867AbjFJIbk (ORCPT ); Sat, 10 Jun 2023 04:31:40 -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 E004F2718; Sat, 10 Jun 2023 01:31:37 -0700 (PDT) X-GND-Sasl: alexandre.belloni@bootlin.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1686385896; 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=OK8Q4QRjn4O3LEpDvvgIC+0ZRQV/BQxETmAgTgYPCO4=; b=BWM/pGjsGVLKFet0yE0Oc813Y+lJ4mUt1mo2P6/srAsGiMNPRquuzfFbFBdYg58xLvI5u4 gZHmp0dtrZ7YPXW5GrvbV1/jy1zt6/Vx4Umrt83vLzXHaAojtJLnaEAYRUjUbUJTjyUyAv 9Teqk4e2enhoNCBhDuZ++UdaIZNyKPvJzrLkoGrv3eOHMaiFuy5prYf+Rge8E7Xii+HUSG 7QK9c96p5CFgImZZ7MwK6ViOCPV/XkxZLf1XBYfa1mHYJQAOJVuxDyTnulpAjc4IKWPJdm 7MaiIKAPlPYzY2FL2mujx5bwn7CUm21IVnrpu9mBupkXIXlKcNZhzf5OY9+XkA== X-GND-Sasl: alexandre.belloni@bootlin.com X-GND-Sasl: alexandre.belloni@bootlin.com X-GND-Sasl: alexandre.belloni@bootlin.com Received: by mail.gandi.net (Postfix) with ESMTPSA id 25D07C0005; Sat, 10 Jun 2023 08:31:36 +0000 (UTC) Date: Sat, 10 Jun 2023 10:31:35 +0200 From: Alexandre Belloni To: Jan Kiszka Cc: Alessandro Zummo , linux-rtc@vger.kernel.org, Linux Kernel Mailing List Subject: Re: [PATCH] rtc: pcf-8563: Report previously detected low-voltage via RTC_VL_BACKUP_LOW Message-ID: <20230610083135e40dd2f6@mail.local> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Jan, On 09/06/2023 23:04:12+0200, Jan Kiszka wrote: > From: Jan Kiszka > > The VL bit in the seconds register remains set only until seconds are > written under main power. As this often happens during boot-up after > picking up a network time, make sure to preserve the low battery state > across this, caching it and returning it via the RTC_VL_BACKUP_LOW bit. > > To permit userspace clearing this state during runtime, also implement > RTC_VL_CLR that works against the cached state. > > This is emulating RTCs which have a battery voltage check that works > under main power as well. > Emulating doesn't work well and I deliberately chose to not implement it. For example, in your scenario, if you boot twice without using VL_READ, you anyway have lost the information. This makes emulating unreliabl. The fix you need is in userspace where you have to ensure you read the status before setting the time. > Signed-off-by: Jan Kiszka > --- > drivers/rtc/rtc-pcf8563.c | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) > > diff --git a/drivers/rtc/rtc-pcf8563.c b/drivers/rtc/rtc-pcf8563.c > index 7e720472213c..f8c6cdb9a39d 100644 > --- a/drivers/rtc/rtc-pcf8563.c > +++ b/drivers/rtc/rtc-pcf8563.c > @@ -81,6 +81,7 @@ struct pcf8563 { > #ifdef CONFIG_COMMON_CLK > struct clk_hw clkout_hw; > #endif > + bool low_bat; > }; > > static int pcf8563_read_block_data(struct i2c_client *client, unsigned char reg, > @@ -207,6 +208,7 @@ static int pcf8563_rtc_read_time(struct device *dev, struct rtc_time *tm) > return err; > > if (buf[PCF8563_REG_SC] & PCF8563_SC_LV) { > + pcf8563->low_bat = true; > dev_err(&client->dev, > "low voltage detected, date/time is not reliable.\n"); > return -EINVAL; > @@ -277,6 +279,8 @@ static int pcf8563_rtc_set_time(struct device *dev, struct rtc_time *tm) > static int pcf8563_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg) > { > struct i2c_client *client = to_i2c_client(dev); > + struct pcf8563 *pcf8563 = i2c_get_clientdata(client); > + unsigned int state = 0; > int ret; > > switch (cmd) { > @@ -284,9 +288,16 @@ static int pcf8563_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long > ret = i2c_smbus_read_byte_data(client, PCF8563_REG_SC); > if (ret < 0) > return ret; > - > - return put_user(ret & PCF8563_SC_LV ? RTC_VL_DATA_INVALID : 0, > - (unsigned int __user *)arg); > + if (ret & PCF8563_SC_LV) { > + state |= RTC_VL_DATA_INVALID; > + pcf8563->low_bat = true; > + } > + if (pcf8563->low_bat) > + state |= RTC_VL_BACKUP_LOW; > + return put_user(state, (unsigned int __user *)arg); > + case RTC_VL_CLR: > + pcf8563->low_bat = false; > + return 0; > default: > return -ENOIOCTLCMD; > } > -- > 2.35.3 -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com