Re: [PATCH] Fix efifb initialisation when the only GOP device implements ConOut.

[David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

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On Mon, 2013-01-07 at 19:16 +0000, Matthew Garrett wrote:
> On Mon, Jan 07, 2013 at 07:12:51PM +0000, David Woodhouse wrote:
> > On Mon, 2013-01-07 at 18:43 +0000, Matthew Garrett wrote:
> > > The kernel does, the EFI boot stub doesn't. There's probably an argument 
> > > for having it fail in that case, but it wouldn't even be able to print 
> > > an error message without some gymnastics.
> > 
> > Printing an error message is simple enough from assembler; you just need
> > to call sys_table->con_out->output_string.
> 
> I don't think that's guaranteed to do something unless we've set a 
> console mode first, but sure, that ought to be an improvement.

It's what we do for efi_printk() in all other cases where the EFI stub
bails out. It's certainly fair enough as a best-effort.

> >  "Sorry, this kernel cannot boot in " (32|64) "-bit mode this way. Your
> > bootloader should have ignored the shiny new EFI handover protocol and
> > booted it the old way. It would have worked then, albeit without EFI
> > runtime services. Which you probably wouldn't have missed."
> 
> "(32|64) bit kernels cannot be booted via the EFI handover 
> protocol on (64|32) bit firmware"?

Yeah. But the bootloader *could* have booted this kernel, if it had just
chosen to use the old handover protocol. And right now, there's no way
for the bootloader to *tell* what it should do.

It wouldn't be impossible to simply have both 32-bit and 64-bit stubs
(conditionally) present in the kernel, and support both simultaneously.
But if we can't do that, then I suspect we should at *least* make sure
we let the bootloader know which one *is* available, so it doesn't end
up calling the wrong one.

Perhaps we should declare that handover_offset is for the 64-bit stub,
and add a handover_offset32 for the 32-bit stub?

-- 
dwmw2


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