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Ahmad Fatoum c27fee16fa 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 d3700b6b64 ("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: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220426071056.1187235-4-s.hauer@pengutronix.de
 		2022-06-24 21:24:02 +02:00
Documentation A single featurelet for delay accounting. Delayed a bit 2022-06-05 16:58:27 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
arch Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
block for-5.19/drivers-2022-06-02 2022-06-03 10:25:56 -07:00
certs Kbuild updates for v5.19 2022-05-26 12:09:50 -07:00
crypto This update includes the following changes: 2022-05-27 18:06:49 -07:00
drivers rtc: rv8803: re-initialize all Epson RX8803 registers on voltage loss 2022-06-24 21:24:02 +02:00
fs fix for breakage in #work.fd this window 2022-06-05 17:14:03 -07:00
include A single featurelet for delay accounting. Delayed a bit 2022-06-05 16:58:27 -07:00
init This set of changes updates init and user mode helper tasks to be 2022-06-03 16:03:05 -07:00
ipc These changes update the ipc sysctls so that they are fundamentally 2022-06-03 15:54:57 -07:00
kernel A single featurelet for delay accounting. Delayed a bit 2022-06-05 16:58:27 -07:00
lib Bitmap patches for 5.19-rc1 2022-06-04 14:04:27 -07:00
mm Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
net bluetooth: don't use bitmaps for random flag accesses 2022-06-05 16:28:41 -07:00
samples drm for 5.19-rc1 2022-05-25 16:18:27 -07:00
scripts A set of objtool fixes: 2022-06-05 09:45:27 -07:00
security Cleanups (and one fix) around struct mount handling. 2022-06-04 19:00:05 -07:00
sound USB / Thunderbolt changes for 5.19-rc1 2022-06-03 11:17:49 -07:00
tools A single featurelet for delay accounting. Delayed a bit 2022-06-05 16:58:27 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt VFIO updates for v5.19-rc1 2022-06-01 13:49:15 -07:00
.clang-format clang-format: Fix space after for_each macros 2022-05-20 19:27:16 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
Makefile Linux 5.19-rc1 2022-06-05 17:18:54 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.