On 22/02/2021 22:20:47+0100, Alexandre Belloni wrote:

On 22/02/2021 18:12:42+0100, Sebastian Reichel wrote:

quoted

Congatec's QMX6 system on module (SoM) uses a m41t62 as RTC. The
modules SQW clock output defaults to 32768 Hz. This behaviour is
used to provide the i.MX6 CKIL clock. Once the RTC driver is probed,
the clock is disabled and all i.MX6 functionality depending on
the 32 KHz clock has undefined behaviour. On systems using hardware
watchdog it seems to likely trigger a lot earlier than configured.

The proper solution would be to describe this dependency in DT,
but that will result in a deadlock. The kernel will see, that
i.MX6 system clock needs the RTC clock and do probe deferral.
But the i.MX6 I2C module never becomes usable without the i.MX6
CKIL clock and thus the RTC's clock will not be probed. So from
the kernel's perspective this is a chicken-and-egg problem.

Reading the previous paragraph, I was going to suggest describing the
dependency and wondering whether this would cause a circular dependency.
I guess this will keep being an issue for clocks on an I2C or SPI bus...

quoted

Technically everything is fine by not touching anything, since
the RTC clock correctly enables the clock on reset (i.e. on
battery backup power loss) and also the bootloader enables it
in case a kernel without this support has been booted.

The 'protected-clocks' property is already in use for some clocks
that may not be touched because of firmware limitations and is
described in Documentation/devicetree/bindings/clock/clock-bindings.txt.

Signed-off-by: Sebastian Reichel <redacted>

Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Or maybe you expected me to apply the patch, how are the following
patches dependent on this one?


-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com