On 22/02/2021 22:20:47+0100, Alexandre Belloni wrote: > On 22/02/2021 18:12:42+0100, Sebastian Reichel wrote: > > 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... > > > 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 <sebastian.reichel@xxxxxxxxxxxxx> > Acked-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> 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
