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Date:   Thu, 5 Jan 2023 12:35:34 +0100
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Alexander Stein <alexander.stein@ew.tq-group.com>
Cc:     Michael Walle <michael@walle.cc>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        Dan Carpenter <error27@gmail.com>
Subject: Re: [PATCH v5 00/21] nvmem: core: introduce NVMEM layouts
Message-ID: <20230105123534.38a70640@xps-13>
In-Reply-To: <2143916.GUh0CODmnK@steina-w>
References: <20221206200740.3567551-1-michael@walle.cc>
        <20230103163902.218cb5c7@xps-13>
        <cf00e248-1f2c-d4ce-868d-9f77b2c9b76f@linaro.org>
        <2143916.GUh0CODmnK@steina-w>
Organization: Bootlin
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Hello,

alexander.stein@ew.tq-group.com wrote on Thu, 05 Jan 2023 12:04:52
+0100:

> Am Dienstag, 3. Januar 2023, 16:51:31 CET schrieb Srinivas Kandagatla:
> > Hi Miquel,
> >=20
> > On 03/01/2023 15:39, Miquel Raynal wrote: =20
> > > Hi Srinivas,
> > >=20
> > > michael@walle.cc wrote on Tue,  6 Dec 2022 21:07:19 +0100: =20
> > >> This is now the third attempt to fetch the MAC addresses from the VPD
> > >> for the Kontron sl28 boards. Previous discussions can be found here:
> > >> https://lore.kernel.org/lkml/20211228142549.1275412-1-michael@walle.=
cc/
> > >>=20
> > >>=20
> > >> NVMEM cells are typically added by board code or by the devicetree. =
But
> > >> as the cells get more complex, there is (valid) push back from the
> > >> devicetree maintainers to not put that handling in the devicetree.
> > >>=20
> > >> Therefore, introduce NVMEM layouts. They operate on the NVMEM device=
 and
> > >> can add cells during runtime. That way it is possible to add more co=
mplex
> > >> cells than it is possible right now with the offset/length/bits
> > >> description in the device tree. For example, you can have post proce=
ssing
> > >> for individual cells (think of endian swapping, or ethernet offset
> > >> handling).
> > >>=20
> > >> The imx-ocotp driver is the only user of the global post processing =
hook,
> > >> convert it to nvmem layouts and drop the global post pocessing hook.
> > >>=20
> > >> For now, the layouts are selected by the device tree. But the idea is
> > >> that also board files or other drivers could set a layout. Although =
no
> > >> code for that exists yet.
> > >>=20
> > >> Thanks to Miquel, the device tree bindings are already approved and
> > >> merged.
> > >>=20
> > >> NVMEM layouts as modules?
> > >> While possible in principle, it doesn't make any sense because the N=
VMEM
> > >> core can't be compiled as a module. The layouts needs to be availabl=
e at
> > >> probe time. (That is also the reason why they get registered with
> > >> subsys_initcall().) So if the NVMEM core would be a module, the layo=
uts
> > >> could be modules, too. =20
> > >=20
> > > I believe this series still applies even though -rc1 (and -rc2) are o=
ut
> > > now, may we know if you consider merging it anytime soon or if there
> > > are still discrepancies in the implementation you would like to
> > > discuss? Otherwise I would really like to see this laying in -next a
> > > few weeks before being sent out to Linus, just in case. =20
> >=20
> > Thanks for the work!
> >=20
> > Lets get some testing in -next. =20
>=20
> This causes the following errors on existing boards (imx8mq-tqma8mq-
> mba8mx.dtb):
> root@tqma8-common:~# uname -r
> 6.2.0-rc2-next-20230105
>=20
> > OF: /soc@0: could not get #nvmem-cell-cells for /soc@0/bus@30000000/ =20
> efuse@30350000/soc-uid@4
> > OF: /soc@0/bus@30800000/ethernet@30be0000: could not get #nvmem-cell-ce=
lls  =20
> for /soc@0/bus@30000000/efuse@30350000/mac-address@90
>=20
> These are caused because '#nvmem-cell-cells =3D <0>;' is not explicitly s=
et in=20
> DT.
>=20
> > TI DP83867 30be0000.ethernet-1:0e: error -EINVAL: failed to get nvmem c=
ell  =20
> io_impedance_ctrl
> > TI DP83867: probe of 30be0000.ethernet-1:0e failed with error -22 =20
>=20
> These are caused because of_nvmem_cell_get() now returns -EINVAL instead =
of -
> ENODEV if the requested nvmem cell is not available.

Should we just assume #nvmem-cell-cells =3D <0> by default? I guess it's
a safe assumption.

Thanks,
Miqu=C3=A8l