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Date: Wed, 27 Nov 2013 15:01:04 +0100
From: Laszlo Ersek <lersek@redhat.com>
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Subject: Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than
 one flash drive
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To: Markus Armbruster <armbru@redhat.com>
Cc: "edk2-devel@lists.sourceforge.net" <edk2-devel@lists.sourceforge.net>, Jordan Justen <jljusten@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Cole Robinson <crobinso@redhat.com>

On 11/27/13 14:52, Markus Armbruster wrote:
> Jordan Justen <jljusten@gmail.com> writes:
> 
>> On Tue, Nov 26, 2013 at 5:32 AM, Laszlo Ersek <lersek@redhat.com> wrote:
>>> On 11/26/13 13:36, Markus Armbruster wrote:
>>>
>>>> Your stated purpose for multiple -pflash:
>>>>
>>>>     This accommodates the following use case: suppose that OVMF is split in
>>>>     two parts, a writeable host file for non-volatile variable storage, and a
>>>>     read-only part for bootstrap and decompressible executable code.
>>>>
>>>> Such a split between writable part and read-only part makes sense to me.
>>>> How is it done in physical hardware?  Single device with configurable
>>>> write-protect, or two separate devices?
>>>
>>> (Jordan could help more.)
>>>
>>> Likely one device that's fully writeable.
>>
>> Most parts will have a dedicated read-only line.
>>
>> Many devices have 'block-locking' that will make some subset of blocks
>> read-only until a reset.
>>
>> In addition to this, many chipsets will allow flash writes to be
>> protected by triggering SMM when a flash write occurs.
>>
>> Using multiple chips are less common due to cost, but this is not a
>> factor for QEMU. :)
> 
> Should we stick to what real hardware does?  Single device, perhaps with
> block locking.

I can't back a single flash device with two drives (= two host-side
files), which is the incentive for this change.

Thanks
Laszlo