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SubjectRe: [PATCH v3 00/14] rtc: pcf2127: add PCF2131 driver

I know I've been holding off on the review of this series for a while
and I'm sorry for that.

One of the main issue that is remaining is that the driver ends up being
53% bigger and generaly less efficient for no added functionality for
the existing RTCs.

I know performance is not a concern however, having more code in the
set/read time and irq paths means that it is more difficult to set an
get the time precisely.

I guess I'll take it as a merged driver but I took a different decision
for other RTCs.

On 15/12/2022 10:02:01-0500, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <>
> Hello,
> this patch series adds the driver for the PCF2131 real-time clock.
> This RTC is very similar in functionality to the PCF2127/29 with the
> following differences:
> -supports two new control registers at offsets 4 and 5
> -supports a new reset register
> -supports 4 tamper detection functions instead of 1
> -has no nvmem (like the PCF2129)
> -has two output interrupt pins instead of one
> -has 1/100th seconds capabilities (not supported in this driver)
> -pcf2127 has watchdog clock sources: 1/60, 1, 64 and 4096Hz
> pcf2131 has watchdog clock sources: 1/64, 1/4, 4 and 64Hz
> -watchdog value register cannot be read after being set
> Most of the register addresses are very different, although they still
> follow the same layout. For example, the time/date and tamper registers
> have a different base address, but the offsets are all the same.
> Consequently, the source code of the PCF2127 driver can be easily adapted
> to support this new device.
> Patches 1 to 6 modify the existing pcf2127 driver to make it more generic
> and able to support multiple variants, like the PCF2131. This is done
> mostly by using offsets instead of absolute hardcoded register addresses.
> Patch 7 add actual support for the PCF2131.
> Patch 8 configures all interrupt sources to go through the INT A pin.
> Patch 9 changes the PWRMNG bits to be the same with the PCF2131 as they
> are with the PCF2127/29 (different default values).
> Patch 10 allow to confirm PCF2131 device presence by reading the reset
> register fixed pattern.
> Patch 11 adapt the time/date registers write sequence for PCF2131 (STOP and
> CPR bits).
> Patch 12 add support for generic watchdog timing configuration.
> Patch 13 add a new flag to identify if device has read support for reading
> watchdog register value.
> Since the watchdog value register cannot be read on the PCF2131 after
> being set, it seems that we cannot detect if watchdog timer was
> started by bootloader. I am not sure what is the best way to handle
> this situation, suggestions are welcomed.
> Patch 14 add the dt-bindings for the PCF2131.
> I have tested the driver using a PCF2131-ARD evaluation board connected to
> an NXP imx8mp evaluation board:
> - Time get/set ok;
> - Alarms get/set ok
> - Timestamp 1 to 4 ok
> - IRQ alarm ok
> - Watchdog ok
> - Also tested successfully with "RTC Driver Test Example" from
> Documentation/rtc.txt
> I have also tested the driver on a custom PCF2129 adapter board connected to a
> beaglebone black.
> Thank you.
> Link: [v1]
> Link: [v2]
> Changes for V3:
> - Rebased for kernel v6.1
> Changes for V2:
> - In general, fix and improvements after I have tested on real hardware
> - Fix alarm interrupt A/B mask setting for PCF2131:
> PCF2131_BIT_INT_AIE must be cleared, not set, to enable interrupt.
> - Remove low_reg validation: only check if TS interrupt flag is
> defined, as low_reg is defined at address 0 for PCF2127/29.
> - Change PWRMNG value for PCF2131: default is different than PCF2127/29.
> - Adapt time/date registers write sequence for PCF2131 (STOP and CPR bits).
> - Map all interrupt sources to INT A pin
> - Read and validate PCF2131 device presence from RESET register
> - Adapt watchdog configuration for PCF2131
> Hugo Villeneuve (14):
> rtc: pcf2127: add variant-specific configuration structure
> rtc: pcf2127: adapt for time/date registers at any offset
> rtc: pcf2127: adapt for alarm registers at any offset
> rtc: pcf2127: adapt for WD registers at any offset
> rtc: pcf2127: adapt for CLKOUT register at any offset
> rtc: pcf2127: add support for multiple TS functions
> rtc: pcf2127: add support for PCF2131 RTC
> rtc: pcf2127: add support for PCF2131 interrupts on output INT_A
> rtc: pcf2127: set PWRMNG value for PCF2131
> rtc: pcf2127: read and validate PCF2131 device signature
> rtc: pcf2127: adapt time/date registers write sequence for PCF2131
> rtc: pcf2127: support generic watchdog timing configuration
> rtc: pcf2127: add flag for watchdog register value read support
> dt-bindings: rtc: pcf2127: add PCF2131
> .../devicetree/bindings/rtc/nxp,pcf2127.yaml | 4 +-
> drivers/rtc/Kconfig | 4 +-
> drivers/rtc/rtc-pcf2127.c | 939 ++++++++++++++----
> 3 files changed, 752 insertions(+), 195 deletions(-)
> --
> 2.30.2

Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering

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