Re: [PATCH] Pass barebox version to kernel

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Feb 27, 2018 at 10:43:59PM +0300, Peter Mamonov wrote:
> On Tue, Feb 27, 2018 at 09:34:30AM +0100, Sascha Hauer wrote:
> > Hi Peter,
> > 
> > On Mon, Feb 26, 2018 at 01:12:02PM +0300, Peter Mamonov wrote:
> > > Hi, Sasha,
> > > 
> > > On Mon, Feb 26, 2018 at 09:23:49AM +0100, Sascha Hauer wrote:
> > > > When userspace is interested in the barebox version it has currently no
> > > > way of reliably reading it. Add it to the kernel command line as it's an
> > > > established way to pass information from the bootloader to the kernel.
> > > > If CONFIG_FLEXIBLE_BOOTARGS is enabled then the barebox version is
> > > > passed in the "bootloader.version=" variable.
> > > 
> > > Some time ago we solved a similar problem: a number of parameters including 
> > > barebox version, MAC address (which may be random due to the lack of a NIC 
> > > EEPROM) and some vendor specific parameters are passed to the kernel via DTB.  
> > > A dedicated command was implemented which can either patch the existing DTB or 
> > > generate an overlay DTB.  In the latter case the overlay DTB is passed to the 
> > > kernel with the help of a new `bootm` option. Of course the latter approach 
> > > requires support on the kernel side.
> > 
> > We could of course pass the barebox version in the /chosen node. That
> > would require a of_register_fixup(). Why would we need an extra command
> > for that?
> 
> Well, it allows some extra flexibility: either original DTB is patched or a
> separate DTB blob is generated. However there is no strict need for a command.
> 
> My actual point is that passing various bootloader stuff to a kernel via DTB
> feels like a cleaner solution, rather than using kernel cmdline for that
> purpose.

I tend to buy that argument. Especially when the stuff the bootloader
wants to pass becomes more and more then the device tree seems like a
good place. The downside is that not all boards have a devicetree (not
counting legacy boards here, but for example UEFI boards).

Any other opinions? We could also do both. If we only pass the version
then this would be ok I guess, but I have no idea where this leads to.

Sascha

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