linux-kernel - Re: [Xen-devel] [PATCH] xen/hvc-console: Make it work with HVM guests.

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Message-ID: <20131028154837.GC4353@phenom.dumpdata.com>
Date:	Mon, 28 Oct 2013 11:48:37 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	Julien Grall <julien.grall@...aro.org>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] [PATCH] xen/hvc-console: Make it work with HVM
 guests.

On Sat, Oct 26, 2013 at 09:27:08AM +0100, Ian Campbell wrote:
> On Fri, 2013-10-25 at 15:38 -0400, Konrad Rzeszutek Wilk wrote:
> > On Thu, Oct 24, 2013 at 05:43:54PM +0100, Ian Campbell wrote:
> > > But stepping back how/why is this function called on x86 when not
> > > running under Xen? Wouldn't the use have to be using console=hvc or
> > > earlyprintk=xen or something -- which strikes me as user error... IOW
> > > can we not just nuke the check
> > 
> > It shouldn't - ever. On x86 it is called from the early PV bootup code.
> > 
> > I occasionaly use it when developing/debugging and as such want it working
> > in HVM even during early bootup.
> 
> Does earlyprintk=ttyS0,cough not Just Work for HVM guests? That would
> avoid all of this stuff and assuming it works would be preferable IMHO.

It works OK. But this is an alternative avenue of using 'xen_raw_printk'
for both PV and HVM.

> 
> Anyway, if not, then given that the xen_cpuid_base case is entirely x86
> specific perhaps we can abstract this as something like:
> 
> 	if (xen_arch_raw_console(str))
> 		return
> 
> 	dom0_write_console(...)
> 
> Then ARM:
> 	#define xen_arch_raw_console 0
> and x86
> 	static inline int xen_arch_raw_console(str)
> 	{
> 		if (xen_domain())
> 			return 0;
> 
> 		/* Do the outb thing */
> 		return 1;
> 	}
> 
> This would also avoid the need for #ifdef x86 in the main function which
> Julien pointed out.

OK.
> 
> Ian.
> 
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