linux-kernel - Re: Exposing nvmem cells to userspace?

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Message-ID: <20220923103333.78c7a19b@xps-13>
Date:   Fri, 23 Sep 2022 10:33:33 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Robert Marko <robert.marko@...tura.hr>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-kernel@...r.kernel.org
Subject: Re: Exposing nvmem cells to userspace?

Hi Srinivas,

srinivas.kandagatla@...aro.org wrote on Thu, 22 Sep 2022 22:33:52 +0100:

> On 22/09/2022 11:23, Miquel Raynal wrote:
> > Hello Srinivas,
> > 
> > I am currently looking at the Open Compute Project ONIE Tlv tables in
> > modern networking hardware. Thanks to the specification being available
> > for many years and rather easy to implement, those tables are already
> > present in many switches. Manufacturers just have to provide a small
> > storage medium exposing factory-related information (manufacturer, date,
> > serial#, mac addresses, etc) in Type-Length-Value fields, as well
> > as their own extensions if they want. These tables are common, but
> > there is currently no shared decoding logic, each provider maintaining
> > its own internally.
> > 
> > I am currently looking for upstreaming an nvmem layout driver for
> > exposing the standard nvmem cells. This way, Ethernet drivers might eg.
> > take the base MAC address from there. But I feel like there is
> > something missing, because the vendor name, the device version, the
> > serial number or any other information available in these tables might
> > also very well be used by the userspace rather than the kernel drivers
> > only.  
> 
> Could you explain the userspace side use-case?

Right now I don't have any TBH. But in general, having access to a
serial number, a manufacturing date, a hardware batch or whatever other
per-device factory information is always useful.

> > Thus, I was wondering if there was some ongoing work to make these
> > cells available to userspace (in /sys maybe?) or if this had already
> > been discussed somewhere. Otherwise, would you be open to such a  
> 
> we had this discussed this in many instances and this is some thing we would desire to have but we never got it moving forward.

Ok.

> > contribution? I guess it would also be a useful debug tool anyway (and
> > might very well be moved somewhere else than in /sys).  
> 
> getting sysfs working correctly in sync with userspace might be tricky in this particular case as we will be creating cells after the provider driver is created.
> 
> debugfs on the other hand is more doable.

Ok, I might try something with debugfs then. I'll keep this in mind.

Thanks,
Miquèl