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

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Message-ID: <YJFpZzm07ZX3aYsK@piout.net>
Date:   Tue, 4 May 2021 17:33:59 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Samuel Holland <samuel@...lland.org>,
        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 30/04/2021 11:02:06+0200, 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 would think nvmem is still the proper subsystem. I guess maybe we
should have a version of __nvmem_device_get that would ensure exclusive
access to a cell, thus preventing userspace accessing it as long a the
kernel is using it.

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