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Date:   Sun, 1 Oct 2023 17:59:42 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.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>
Subject: Re: [PATCH v10 3/3] nvmem: core: Expose cells through sysfs
Message-ID: <20231001175942.749d9bb3@xps-13>
In-Reply-To: <5f1221613fb71b87c01c82add9fe5097@milecki.pl>
References: <20230922174854.611975-1-miquel.raynal@bootlin.com>
        <20230922174854.611975-4-miquel.raynal@bootlin.com>
        <1a27a3341379b9679174f7c5143bbeb3@milecki.pl>
        <5f1221613fb71b87c01c82add9fe5097@milecki.pl>
Organization: Bootlin
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Hi Rafa=C5=82,

rafal@milecki.pl wrote on Fri, 29 Sep 2023 07:18:32 +0200:

> On 2023-09-28 17:31, Rafa=C5=82 Mi=C5=82ecki wrote:
> > On 2023-09-22 19:48, Miquel Raynal wrote: =20
> >> The binary content of nvmem devices is available to the user so in the
> >> easiest cases, finding the content of a cell is rather easy as it is
> >> just a matter of looking at a known and fixed offset. However, nvmem
> >> layouts have been recently introduced to cope with more advanced
> >> situations, where the offset and size of the cells is not known in
> >> advance or is dynamic. When using layouts, more advanced parsers are
> >> used by the kernel in order to give direct access to the content of >>=
 each
> >> cell, regardless of its position/size in the underlying
> >> device. Unfortunately, these information are not accessible by users,
> >> unless by fully re-implementing the parser logic in userland. =20
> >> >> Let's expose the cells and their content through sysfs to avoid the=
se =20
> >> situations. Of course the relevant NVMEM sysfs Kconfig option must be
> >> enabled for this support to be available. =20
> >> >> Not all nvmem devices expose cells. Indeed, the .bin_attrs attribut=
e =20
> >> group member will be filled at runtime only when relevant and will
> >> remain empty otherwise. In this case, as the cells attribute group >> =
will
> >> be empty, it will not lead to any additional folder/file creation. =20
> >> >> Exposed cells are read-only. There is, in practice, everything in t=
he =20
> >> core to support a write path, but as I don't see any need for that, I
> >> prefer to keep the interface simple (and probably safer). The >> inter=
face
> >> is documented as being in the "testing" state which means we can later
> >> add a write attribute if though relevant. =20
> >> >> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com> =20
> >=20
> > Tested-by: Rafa=C5=82 Mi=C5=82ecki <rafal@milecki.pl>
> >=20
> > # hexdump -C /sys/bus/nvmem/devices/u-boot-env0/cells/ipaddr@15c
> > 00000000  31 39 32 2e 31 36 38 2e  31 2e 31                 > |192.168.=
1.1|
> > 0000000b =20
>=20
> The same test after converting U-Boot env into layout driver:
>=20
> # hexdump -C /sys/bus/nvmem/devices/mtd1/cells/ipaddr@15c
> 00000000  31 39 32 2e 31 36 38 2e  31 2e 31                 |192.168.1.1|
> 0000000b
>=20
> Looks good!
>=20

Great! Thanks a lot for testing!

Miqu=C3=A8l