Re: [Xen-devel] [RFC 6/6] xen/arm: Replace early_printk call to printk call

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 20/02/14 11:20, Ian Campbell wrote:
> On Thu, 2014-02-20 at 11:14 +0000, Julien Grall wrote:
> > On 20/02/14 11:05, Ian Campbell wrote:
> > > On Thu, 2014-02-20 at 11:01 +0000, Julien Grall wrote:
> > > > On 20/02/14 09:04, Ian Campbell wrote:
> > > > > I was actually thinking more along the lines of a .word at a defined
> > > > > offset which you could hex edit to a specific value to activate a
> > > > > particular flavour of early printk handling. That would be sufficient
> > > > > e.g. for osstest to activate the appropriate stuff for the specific
> > > > > platform.
> > > > I don't see useful use case to have a such early printk implementation
> > > > in Xen. When the board is fully supported, failed at early stage (e.g
> > > > before console is initialized) is very unlikely. At least if you don't
> > > > play with memory.
> > > a) there are boards which aren't fully supported, getting some debug out
> > > of a distro package might be useful
> > Few months ago we have decided to allow early printk only when Xen is
> > compiled with debug enabled. It seems a big mistake to ship distro with
> > debug enabled :).
> This was because earlyprintk only supports a static single configuration
> at compile time. If that restriction was lifted then there would be no
> reason to limit earlyprintk to debug builds.
>
> > > b) even for boards which are fully supported there may still be bugs
> > > which only appear under particular circumstances.
> > I understand this use case. If I understand your previous mail the
> > solution would me "Hex editing manually the Xen binary to set the early
> > printk", right? If so, you are assuming that the distro (or anything
> > else) is proving the zImage. Otherwise the developper has to:
> >      - unpack from the uImage
> >      - editing the zImage
> >      - recreate the uImage
> No distro would ship the actual uImage, it's too machine specific.
>
> I would expect this to be used by running:
>         xen-enable-early-printk /boot/xen midway
>
> where xen-enable-early-printk is a simple tool we provide.
And a similar one to disable, I guess.

> Then if a uIamge is then required then this would be generated by
> whatever distro tooling would have generated it in the non-early-printk
> case, by rerunning that tool.
Sounds good. Do you plan to work on it?

It would be nice to have this item on the ARM todo page.

--
Julien Grall

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