linux-kernel - Re: [PATCH] rtc: sun6i: Add NVMEM provider

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Date:   Mon, 10 May 2021 10:00:46 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: sun6i: Add NVMEM provider

On 09/05/2021 22:39:30-0500, Samuel Holland wrote:
> On 4/30/21 4:02 AM, Maxime Ripard wrote:
> > Hi,
> > 
> > On Sun, Apr 18, 2021 at 08:45:49PM -0500, Samuel Holland wrote:
> >> 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@...lland.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