linux-kernel - Re: [PATCH v6 3/3] nvmem: core: Expose cells through sysfs

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Message-ID: <20230717184117.065e9585@xps-13>
Date:   Mon, 17 Jul 2023 18:41:17 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Robert Marko <robert.marko@...tura.hr>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v6 3/3] nvmem: core: Expose cells through sysfs

Hi Michael,

michael@...le.cc wrote on Mon, 17 Jul 2023 14:24:45 +0200:

> Hi,
> 
> > 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.  
> 
> What is the difference between manual loading with insmod and automatic
> module loading? Or is the limitation, layout as M and device driver as Y
> doesn't work?

The nvmem core uses usermodehelper to load the relevant layout
module, but that only works if the module was installed correctly (make
modules_install).

The limitation is:
* Any storage device driver that registers an nvmem interface =y (or =m
  but loaded before the nvmem layout)
* The relevant nvmem layout =m *and* not installed with make
  modules_install

If you see a way to workaround this, let me know, but there is no way
we can enforce Kconfig dependencies between storage drivers and nvmem
layouts IMHO.

Thanks,
Miquèl