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

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Message-ID: <2023100200-snowcap-arena-a548@gregkh>
Date:   Mon, 2 Oct 2023 11:35:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.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>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH v10 1/3] nvmem: core: Rework layouts to become platform
 devices

On Fri, Sep 22, 2023 at 07:48:52PM +0200, 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>

Did I miss why these were decided to be platform devices and not normal
devices on their own "bus" that are attached to the parent device
properly?  Why platform for a dynamic thing?

If I did agree with this, it should be documented here in the changelog
why this is required to be this way so I don't ask the question again in
the future :)

thanks,

greg k-h