Re: [Qemu-devel] [PATCH RFC] spapr: by-pass SLOF when -kernel is provided

From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: David Gibson <david@gibson.dropbear.id.au>,
	Laurent Vivier <lvivier@redhat.com>
Cc: Andrew Jones <drjones@redhat.com>, Thomas Huth <thuth@redhat.com>,
	qemu-ppc@nongnu.org,
	qemu-devel@nongnu.org"Richard W.M. Jones" <rjones@redhat.com>
Subject: Re: [Qemu-devel] [PATCH RFC] spapr: by-pass SLOF when -kernel is provided
Date: Wed, 6 Jul 2016 13:33:49 +1000	[thread overview]
Message-ID: <ce94508f-64d1-a75b-944a-b3cdae3f75c3@ozlabs.ru> (raw)
In-Reply-To: <20160706013529.GT2251@voom.fritz.box>

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On 06/07/16 11:35, David Gibson wrote:
> On Tue, Jul 05, 2016 at 04:42:37PM +0200, Laurent Vivier wrote:
>> As device-tree is now fully built by QEMU, we don't need SLOF
>> anymore if the kernel is provided on the command line.
>>
>> In this case, don't load SLOF and boot directly into the
>> kernel.
>>
>> This saves at least 5 seconds on the boot sequence.
>>
>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> 
> I'm not comfortable applying this.  We actually used to do this ages
> ago, but changed to always running through SLOF, and there were
> reasons for doing so.
> 
> I don't remember exactly what they were, but I think it boiled down to
> slight differences in state between booting from SLOF and booting
> without SLOF leading to confusing errors from the guest kernel.
> 

PCI resource allocation is still done by SLOF (however having them not set
will trigger allocation in the guest but this is rather unexpected
workaround than a feature); "client-architecture-support" won't work
without SLOF either (i.e. compatibile PowerISA 2.0x CPUs).

-- 
Alexey

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