Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:6 as permitted sender) client-ip=2620:137:e000::3:6;
Date:   Mon, 2 Oct 2023 17:16:12 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Michael Walle <michael@walle.cc>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Robert Marko <robert.marko@sartura.hr>,
        Luka Perkov <luka.perkov@sartura.hr>,
        linux-kernel@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
        Chen-Yu Tsai <wenst@chromium.org>,
        Daniel Golle <daniel@makrotopia.org>,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>
Subject: Re: [PATCH v10 1/3] nvmem: core: Rework layouts to become platform
 devices
Message-ID: <20231002171612.067b84a8@xps-13>
In-Reply-To: <2023100200-snowcap-arena-a548@gregkh>
References: <20230922174854.611975-1-miquel.raynal@bootlin.com>
        <20230922174854.611975-2-miquel.raynal@bootlin.com>
        <2023100200-snowcap-arena-a548@gregkh>
Organization: Bootlin
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Hi Greg,

gregkh@linuxfoundation.org wrote on Mon, 2 Oct 2023 11:35:02 +0200:

> 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).
> >=20
> > 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.
> >=20
> > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com> =20
>=20
> 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?

I don't think you missed anything, following the discussion "how to
picture these layouts as devices" I came up with the simplest
approach: using the platform infrastructure. I thought creating my own
additional bus just for that would involve too much code duplication.
I agree the current implementation kind of abuses the platform
infrastructure. I will have a look in order to maybe mutate this into
its own bus.

> 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 :)

Haha, I don't think you did ;)

Thanks,
Miqu=C3=A8l