On 09/05/2021 22:39:30-0500, Samuel Holland wrote:

On 4/30/21 4:02 AM, Maxime Ripard wrote:

quoted

Hi,

On Sun, Apr 18, 2021 at 08:45:49PM -0500, Samuel Holland wrote:

quoted

The sun6i RTC provides 32 bytes of general-purpose data registers.
They can be used to save data in the always-on RTC power domain.
The registers are writable via 32-bit MMIO accesses only.

Expose the region as a NVMEM provider so it can be used by userspace and
other drivers.

Signed-off-by: Samuel Holland <samuel@sholland.org>

As far as I understood, you want to use those registers to implement
super-standby? If so, while it makes sense for the kernel to be able to
be able to write to those registers, I guess it would be a bit unwise to
allow the userspace to access it?

I want the user to be able to pass information to the bootloader (to
select a boot device, e.g. reboot to FEL). I also want the user to be
able to read data stored to these registers by system firmware (e.g.
crust writes exception information there). It's not really related to
standby.

I would want to stack a nvmem-reboot-mode on top to give friendlier
names to some of the numbers, but I don't see a problem with root having
direct access to the registers. It's no different from /dev/nvram
providing access to the PC CMOS RAM.

(which is deprecated in favor of nvmem)


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

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