linux-kernel - Re: [PATCH v10 1/3] nvmem: core: Rework layouts to become platform devices

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Date:   Thu, 28 Sep 2023 22:24:04 +0200
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Walle <michael@...le.cc>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Robert Marko <robert.marko@...tura.hr>,
        Luka Perkov <luka.perkov@...tura.hr>,
        linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Daniel Golle <daniel@...rotopia.org>
Subject: Re: [PATCH v10 1/3] nvmem: core: Rework layouts to become platform
 devices

On 2023-09-22 19:48, Miquel Raynal wrote:
> Current layout support was initially written without modules support in
> mind. When the requirement for module support rose, the existing base
> was improved to adopt modularization support, but kind of a design flaw
> was introduced. With the existing implementation, when a storage device
> registers into NVMEM, the core tries to hook a layout (if any) and
> populates its cells immediately. This means, if the hardware 
> description
> expects a layout to be hooked up, but no driver was provided for that,
> the storage medium will fail to probe and try later from
> scratch. Technically, the layouts are more like a "plus" and, even we
> consider that the hardware description shall be correct, we could still
> probe the storage device (especially if it contains the rootfs).
> 
> One way to overcome this situation is to consider the layouts as
> devices, and leverage the existing notifier mechanism. When a new NVMEM
> device is registered, we can:
> - populate its nvmem-layout child, if any
> - try to modprobe the relevant driver, if relevant
> - try to hook the NVMEM device with a layout in the notifier
> And when a new layout is registered:
> - try to hook all the existing NVMEM devices which are not yet hooked 
> to
>   a layout with the new layout
> This way, there is no strong order to enforce, any NVMEM device 
> creation
> or NVMEM layout driver insertion will be observed as a new event which
> may lead to the creation of additional cells, without disturbing the
> probes with costly (and sometimes endless) deferrals.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>

I rebased & tested my patch converting U-Boot NVMEM device to NVMEM
layout on top of this. It worked!

Tested-by: Rafał Miłecki <rafal@...ecki.pl>

For reference what I used:

partitions {
	partition-loader {
		compatible = "brcm,u-boot";

		partition-u-boot-env {
			compatible = "nvmem-cells";

			nvmem-layout {
				compatible = "brcm,env";

				base_mac_addr: ethaddr {
					#nvmem-cell-cells = <1>;
				};
			};
		};
	};
};

-- 
Rafał Miłecki