Re: [PATCH] rtc: rtc-twl: add NVRAM support

[Tony Lindgren <tony@atomide.com>]

* Ladislav Michl <oss-lists@triops.cz> [230418 12:03]:
> Hi Tony,
> 
> On Tue, Apr 18, 2023 at 12:43:03PM +0300, Tony Lindgren wrote:
> > Hi,
> > 
> > * Ladislav Michl <oss-lists@triops.cz> [230413 12:56]:
> > > Export SRAM using nvmem.
> > 
> > Patch looks good to me, just wondering how this is used..
> 
> This has been sitting in my tree for over five years and it is used
> to store boot state. Patches for u-boot are pending here as well,
> but I'll do my best to upstream reasonable parts of them.
> 
> All was done for failsafe device updating using A/B scheme. Device
> is also using U-Boot's Falcon mode to speed things up, so SPL
> loads kernel directly from UBI volume. To decide which one to load
> and boot, information from NVRAM is used - there is no other memory
> except NVRAM and NAND. I didn't want to use NAND for this purpose,
> see bellow how NVRAM failures are handled.
> 
> > Are we just exporting the nvram via sysfs for userspace to use it
> > for whatever, or is there also some RTC core layer use for it?
> 
> RTC itself is not using it. My board is using RAUC for updates:
> https://rauc.readthedocs.io/en/latest/examples.html#symmetric-a-b-setup

OK thanks for the detailed information :)

Regards,

Tony