Re: [PATCH] schemas: Add schema for firmware logs

["Jan Lübbe" <jlu@pengutronix.de>]

On Mon, 2023-02-06 at 17:32 -0600, Rob Herring wrote:
> +boot-architecture
> 
> On Mon, Feb 6, 2023 at 3:25 PM Simon Glass <sjg@chromium.org> wrote:
> > 
> > Hi Rob,
> > 
> > On Mon, 6 Feb 2023 at 10:15, Rob Herring <robh@kernel.org> wrote:
> > > 
> > > On Sat, Feb 4, 2023 at 6:04 AM Simon Glass <sjg@chromium.org> wrote:
> > > > 
> > > > Hi Peter,
> > > > 
> > > > On Sat, 4 Feb 2023 at 02:36, Peter Robinson <pbrobinson@gmail.com>
> > > > wrote:
> > > > > 
> > > > > Hi Simon,
> > > > > 
> > > > > Does it make sense to devise something that is compatible with the
> > > > > kernel's pstore [1] mechanism?
> > > > 
> > > > Possibly...can you please be a little more specific?
> > > 
> > > Peter is talking about the same thing I suggested on IRC.
> > > 
> > > pstore == ramoops
> > 
> > Oh, I only looked at the DT binding as I thought that was what you
> > were talking about on irc.
> 
> The binding is called ramoops as it's for the RAM backend for pstore.
> 
> My suggestion was either using/extending ramoops or following its
> design as a reserved memory region. All you would need to extend the
> ramoops binding is a new property to define the size of your data.
> 
> > For pstore, isn't the point that Linux wants to save stuff to allow
> > debugging or collection on reboot? What does that have to do with
> > console logs from firmware? That seems like a different thing. Or are
> > you suggesting that we add a pstore driver into U-Boot? It is quite a
> > lot of code, including compression, etc. It might be easier for Linux
> > to write the data into pstore when it starts up?
> 
> Originally ramoops was just what you described. It has grown to
> multiple backends and types of records (hence the rename to pstore).
> If you just add a new subsection within the pstore region, then I
> think the existing kernel infrastructure will support reading it from
> userspace. Maybe new types have to be explicitly supported, IDK.
> 
> U-boot being able to read pstore wouldn't be a terrible feature to
> have anyways if your boot crashes before anything else is up to get
> the output. Note I'd guess the ram backend doesn't do compression as
> supporting slightly corrupted ram is a feature which wouldn't work.

This is basically how it works in Barebox. It can display the pstore contents
after a kernel crash and also (optionally) log to the pstore/ramooms console
log. Slight RAM corruption can be handled by using error correcting codes.

It's not perfect, of course, but still very useful.

Regards,
Jan

> I think any new DT binding is premature and pstore/ramoops was just a
> suggestion to consider. This needs wider consideration of how to
> handle all the various (boot) firmware logs. I've added the
> boot-architecture list for a bit more visibility.

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