Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <da84b6b1-a9d8-ce46-16a9-e1a2d495240c@siemens.com>
Date:   Fri, 9 Jun 2023 23:04:12 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
From:   Jan Kiszka <jan.kiszka@siemens.com>
Subject: [PATCH] rtc: pcf-8563: Report previously detected low-voltage via
 RTC_VL_BACKUP_LOW
Content-Language: en-US
To:     Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        linux-rtc@vger.kernel.org
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?aTNZRWZEeWtKbUNpUlRvKzhLekpKcHNpeEpGVUNnd2xWRzhSd2wrZHN5Ukc0?=
 =?utf-8?B?OFFTWit2anBkbmN0RDR1bnM3L2NrVjZWaWtNYUZGMEI0QXo5N1JQY09FdlRI?=
 =?utf-8?B?c2Urcm1VNU5YYXZObEV2Q1R5NS9aeWs1Z3MrSnJkQzhGZGtqWHZQdUVpSlZO?=
 =?utf-8?B?Z1o3WHA1Y1lua3Y4c3RuNUtaSGxTbzNiVDBiSWFYb2x2Zm5mRk81dUt0alla?=
 =?utf-8?B?RmV4Q1RJeFN4b1Z4dHdwYkpGUUZnUk9nUWdZUDJCRmE5d3huZFRpQ0tBelRL?=
 =?utf-8?B?QWhLa0tsM2FJdlNmVG5KNFhWVWxXZWpBV3JMZitqb0QxOUltRGh6Ny8zd3hP?=
 =?utf-8?B?NkRJdGprY3BaTEt2QlBCVU5aQk9yV1BBclRxK1lhQzZPMkd5T2ZET3hieE1B?=
 =?utf-8?B?ZFczMWFtak5DcW10b3ZMN2FOcC9hZ3MxY2JGQVM4QU9qTlUzaGdNdk02ZCtn?=
 =?utf-8?B?a3hNTm5LRFUxR0RUMWZreCtXMmpaNE1TYzZCM2g3WExIc1lSTVFjVEtTakJD?=
 =?utf-8?B?VGQvZTNjaXEzcFdIbWtKSUdIdFdobHFubGZVUVNOeVlUejBFcGxzUVN4dkd3?=
 =?utf-8?B?cUVDREJhSjNXK1ozK0lOUERWYTgwdlZzM0d1eXdob2VrT3NrMG95RGdFZUY3?=
 =?utf-8?B?MlJVdnZLbGQ3NlRGTUdpbVlJWW9QTXM0WWhtazZhc3pzNGVBcU0xZGNGVTR4?=
 =?utf-8?B?SlZoSTRIRmtEUHFSV1ZESVhiL2hKN0ZaSG5HTkxiRURhZlhjZk5JTmpnMmtr?=
 =?utf-8?B?dDU1ZFlCTm41WFBESC9GN0Fwd2d6dW5DRGRhMzBXbmViNWgrRC80clhtbUhB?=
 =?utf-8?B?VXgzYWpXY0pEaUpDWXhDU0VjaGpYVW94S1cvUmg4T0d3OW9Hc2IzeHFHbS9Y?=
 =?utf-8?B?dGZTSnpZMFo0Q2ZPNlljS3p5RWdMZzc3OUdROW5OOVVGblFVYlZtTnV0OWpS?=
 =?utf-8?B?ZjJKQjkvZlh5UjlQR0JsblhuTjNlRWF0dlJCdEhlRCtxMU1uYWR6MlhlK2kv?=
 =?utf-8?B?a28zeCtFTlpGOW9ieVI1Z2xMWWI3VTNSdzYyTkRlYUFBZm9CWHVyTEV3ZXp2?=
 =?utf-8?B?NXdINUYzUHJmNE9JdzR1SWFDUzVmUGlIZUhoQmtucmFXUldJeUhyRGk3dG9S?=
 =?utf-8?B?UTZnYkFSemZmaEsxUzRQem1xYVFpaVRoZk9CelRoZVBjU0ZPQ0lUb1NKNHBJ?=
 =?utf-8?B?dmlPK29UY0xaMktTRmhyMVlheG1lSVNUNlV0VDBwZ01zTTZyVDRYZmt2MndW?=
 =?utf-8?B?V3ZXNkJEbytkcE5JbG1PMHR2UE5XQXdBTEFYbTRONWpXTkozVjZ5SU9ERWdG?=
 =?utf-8?B?ajFkRXJpMFhNeGYvbnVjN1BtZnNGY3dHbG5iOWo3R2NHZ0Nya05IZks5Ykdl?=
 =?utf-8?B?Yk1XWTJhcXpmZjArd0liZ3Q0S1puSkVPNlNZc2hpTXlFRkpxeEI2RUpxb2hL?=
 =?utf-8?B?U2k5QzFETUVKcEkwZFQ4RUZOOGh2SVlZd0tSNVlZbDVzRG56ak9xT0RlMkdl?=
 =?utf-8?B?ZXMzRnVjK3VuZ3NOd21VY0tXMVVNL0pzbk5MdXBSK0RybXk0eWQ2aXRZVUl0?=
 =?utf-8?B?aVBpcTUwckVLdmVGTks1a3g3dHRiSUJsNDZCM25XTjVrTHhMeWNCcDZGUEhI?=
 =?utf-8?B?bDkwVkxZL0thWEtTd2t4VjkrdGthMldrOGZvM0dTZGtlQVd5Q3NBWEhybHlN?=
 =?utf-8?B?YXZiWFdabXM2eWNNZVNCemZpdEY0Sjk3NmZ6cnplcjIzZE1EN2pZbkhUSEt2?=
 =?utf-8?B?SzZTa1d3Ukd5M1NXSDR4UU5manIrMlBCZlh2THNIMDVSZUFuMkFzTjFuS1V6?=
 =?utf-8?B?M1JDNzhCdmhqQUs0dTYydUZrTjhaWTlEMkZnNk9RSjEvUmtmcDRJeVlxbm5y?=
 =?utf-8?B?OHp1alFtcWtVV1FoQ3hOaEc3UmNrVVJaMEZtekVldVRLclFvdG5iaE1ONWdv?=
 =?utf-8?B?Z2lFZEZpL0Y3L0luWDkxRVphVzZHandUdjFZOTA2S1RtWDAzZWJ0VjlCaitH?=
 =?utf-8?B?L2Rab2tzS05aaEI2SUZTSW9PNGJDZUR3OU1tR3JHT1hGeFhzZDh3dzhyeXlB?=
 =?utf-8?B?dnN2NHNzQnp3YXlpSEd4b1FDV095b3RxMTNyTFE5Ty94OUFxQS9hRkNacE1k?=
 =?utf-8?B?THlobzl4ZHBuOVZYcUtRckJBSUljenpEN29EaElnYXEvQUI2b3RsVStNUmxR?=
 =?utf-8?B?R1E9PQ==?=
X-OriginatorOrg: siemens.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 615d9b18-8006-4f68-34d6-08db692d15db
X-MS-Exchange-CrossTenant-AuthSource: AS4PR10MB6181.EURPRD10.PROD.OUTLOOK.COM
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Jun 2023 21:04:16.5681
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 38ae3bcd-9579-4fd4-adda-b42e1495d55a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: jkg4RELARfWSW2V/vvynImkJOQP8noe9zxoouFJA+2ZLclEDibtIRsgHUKyxaiDNkvCF5m3uFz0l+6x7uNJ+Qw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR10MB7428
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIMWL_WL_MED,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=no autolearn_force=no
        version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

From: Jan Kiszka <jan.kiszka@siemens.com>

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.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 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