From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mslow1.mail.gandi.net (mslow1.mail.gandi.net [217.70.178.240]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D830D71 for ; Mon, 10 May 2021 08:09:56 +0000 (UTC) Received: from relay1-d.mail.gandi.net (unknown [217.70.183.193]) by mslow1.mail.gandi.net (Postfix) with ESMTP id 98DD0D75D7 for ; Mon, 10 May 2021 08:00:57 +0000 (UTC) X-Originating-IP: 90.65.108.55 Received: from localhost (lfbn-lyo-1-1676-55.w90-65.abo.wanadoo.fr [90.65.108.55]) (Authenticated sender: alexandre.belloni@bootlin.com) by relay1-d.mail.gandi.net (Postfix) with ESMTPSA id 3890C240006; Mon, 10 May 2021 08:00:46 +0000 (UTC) Date: Mon, 10 May 2021 10:00:46 +0200 From: Alexandre Belloni To: Samuel Holland Cc: Maxime Ripard , Alessandro Zummo , Chen-Yu Tsai , Jernej Skrabec , linux-rtc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rtc: sun6i: Add NVMEM provider Message-ID: References: <20210419014549.26900-1-samuel@sholland.org> <20210430090206.lybmygrt636nysoc@gilmour> X-Mailing-List: linux-sunxi@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 > > > > 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