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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-02-20 at 11:37 +0000, Julien Grall wrote:
> 
> 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.

Yes, by choosing "none" I suppose.

> > 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?

Not in the immediate future.

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

Done.



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