Commit c27fee16 authored by Ahmad Fatoum's avatar Ahmad Fatoum Committed by Alexandre Belloni
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rtc: rv8803: re-initialize all Epson RX8803 registers on voltage loss 



The reference manuals of both the RX8803 and RV8803 dictate that
"[On V2F/VLF = ] all registers must be initialized".

The RV-8803 application manual (rev. 1.6) further specifies that crossing
V_LOW2 threshold enables flag V2F and triggers a Power-On reset.
According to table 3.11 in the document, all control registers are
defined to sensible values.

However, The Epson RX-8803 doesn't offer the same guarantees.
It explicitly states:

  During the initial power-up, the TEST bit is reset to "0" and the VLF
  bit is set to "1".
  ∗ At this point, all other register values are _undefined_, so be sure to
  perform a reset before using the module.

Commit d3700b6b ("rtc: rv8803: Stop the clock while setting the time")
also had this rationale:

  Indeed, all the registers must be initialized if the voltage has been
  lower than VLOW2 (triggering V2F), but not low enough to trigger a POR.

We should follow the advice and initialize all applicable registers.
We can group the registers into 3 groups:

A) Already correctly handled registers:
  * 0B-0Ch | Timer Counter  | unused and disabled by clearing TE in 0Dh
  * 0Dh    | Extension Reg  | already initialized in rv8803_regs_configure
  * 0Eh    | Flag Reg       | handled in IRQ handler, except for VLF, VDET
  * 0Eh    | VLF, VDET      | cleared in ->set_time
  * 10h    | 100th Seconds  | Already reset via RESET bit
  * 20-21h | Capture Buffer | holds timestamp unused by driver
  * 2Fh    | Event Control  | resets automatically

B) Registers that are hardware initialized on POR, but not on VLF:
  * 0Fh    | Control Reg
  * 2Ch    | OSC Offset

C) RAM that is undefined on voltage loss:
  * 00-06h | Date/Time
  * 07h    | RAM
  * 08-0Ah | Alarm

This means we should initialize after VLF the registers in group B
(RV8803_CTRL and RV8803_OSC_OFFSET).

Group C is all-zero after voltage loss on the RV-8803, but undefined on
the RX-8803. This is ok for Date/Time because ->get_time returns an
error code for as long as the voltage loss flag is active. It's cleared
on ->set_time however. Zeroing both RAM and alarm ensures a fixed value
is read afterwards.

Signed-off-by: default avatarAhmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: default avatarSascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: default avatarAlexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220426071056.1187235-4-s.hauer@pengutronix.de
parent f8176e0b

drivers/rtc/rtc-rv8803.c

+38 −2
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 


#include <linux/bcd.h>

#include <linux/bitops.h>

#include <linux/bitfield.h>

#include <linux/log2.h>

#include <linux/i2c.h>

#include <linux/interrupt.h>
@@ -33,6 +34,7 @@ 
#define RV8803_EXT			0x0D

#define RV8803_FLAG			0x0E

#define RV8803_CTRL			0x0F

#define RV8803_OSC_OFFSET		0x2C



#define RV8803_EXT_WADA			BIT(6)
@@ -49,12 +51,15 @@ 
#define RV8803_CTRL_TIE			BIT(4)

#define RV8803_CTRL_UIE			BIT(5)



#define RX8803_CTRL_CSEL		GENMASK(7, 6)



#define RX8900_BACKUP_CTRL		0x18

#define RX8900_FLAG_SWOFF		BIT(2)

#define RX8900_FLAG_VDETOFF		BIT(3)



enum rv8803_type {

	rv_8803,

	rx_8803,

	rx_8804,

	rx_8900

};
@@ -137,10 +142,41 @@ static int rv8803_write_regs(const struct i2c_client *client, 
	return ret;

}



static int rv8803_regs_init(struct rv8803_data *rv8803)

{

	int ret;



	ret = rv8803_write_reg(rv8803->client, RV8803_OSC_OFFSET, 0x00);

	if (ret)

		return ret;



	ret = rv8803_write_reg(rv8803->client, RV8803_CTRL,

			       FIELD_PREP(RX8803_CTRL_CSEL, 1)); /* 2s */

	if (ret)

		return ret;



	ret = rv8803_write_regs(rv8803->client, RV8803_ALARM_MIN, 3,

				(u8[]){ 0, 0, 0 });

	if (ret)

		return ret;



	return rv8803_write_reg(rv8803->client, RV8803_RAM, 0x00);

}



static int rv8803_regs_configure(struct rv8803_data *rv8803);



static int rv8803_regs_reset(struct rv8803_data *rv8803)

{

	/*

	 * The RV-8803 resets all registers to POR defaults after voltage-loss,

	 * the Epson RTCs don't, so we manually reset the remainder here.

	 */

	if (rv8803->type == rx_8803 || rv8803->type == rx_8900) {

		int ret = rv8803_regs_init(rv8803);

		if (ret)

			return ret;

	}



	return rv8803_regs_configure(rv8803);

}
@@ -631,7 +667,7 @@ static int rv8803_probe(struct i2c_client *client, 
static const struct i2c_device_id rv8803_id[] = {

	{ "rv8803", rv_8803 },

	{ "rv8804", rx_8804 },

	{ "rx8803", rv_8803 },

	{ "rx8803", rx_8803 },

	{ "rx8900", rx_8900 },

	{ }

};
@@ -644,7 +680,7 @@ static const __maybe_unused struct of_device_id rv8803_of_match[] = { 
	},

	{

		.compatible = "epson,rx8803",

		.data = (void *)rv_8803

		.data = (void *)rx_8803

	},

	{

		.compatible = "epson,rx8804",