linux-kernel - Re: [PATCH v4 4/4] nvmem: core: Expose cells through sysfs

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Date:   Thu, 13 Jul 2023 09:42:57 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Robert Marko <robert.marko@...tura.hr>
Subject: Re: [PATCH v4 4/4] nvmem: core: Expose cells through sysfs

Hi Srinivas,

srinivas.kandagatla@...aro.org wrote on Wed, 12 Jul 2023 18:20:01 +0100:

> Hi Miquel,
> 
> On 14/06/2023 07:30, 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.
> > 
> > There is one limitation though: if a layout is built as a module but is
> > not properly installed in the system and loaded manually with insmod
> > while the nvmem device driver was built-in, the cells won't appear in
> > sysfs. But if done like that, the cells won't be usable by the built-in
> > kernel drivers anyway.
> > 
> > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>  
> 
> Unable to apply this, Can you re-base this on rc1?

Yes of course, here it is. I figured out yesterday evening that this
would no longer apply, I did the rebase locally but did not finish
testing. v5 is now in your inbox.

I also split this patch so I now:
- gather all the cells creation together before adding the nvmem device
- then we create the sysfs cells

Cheers,
Miquèl