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Date:   Thu, 28 Sep 2023 17:31:20 +0200
From:   =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <rafal@milecki.pl>
To:     Miquel Raynal <miquel.raynal@bootlin.com>
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
In-Reply-To: <20230922174854.611975-4-miquel.raynal@bootlin.com>
References: <20230922174854.611975-1-miquel.raynal@bootlin.com>
 <20230922174854.611975-4-miquel.raynal@bootlin.com>
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On 2023-09-22 19:48, Miquel Raynal wrote:
> 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.
> 
> Let's expose the cells and their content through sysfs to avoid these
> situations. Of course the relevant NVMEM sysfs Kconfig option must be
> enabled for this support to be available.
> 
> Not all nvmem devices expose cells. Indeed, the .bin_attrs attribute
> 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.
> 
> Exposed cells are read-only. There is, in practice, everything in the
> 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 interface
> is documented as being in the "testing" state which means we can later
> add a write attribute if though relevant.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

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

# 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

-- 
Rafał Miłecki