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Re: [Qemu-devel] [RFC 2/7] fw_cfg dma interface

From: Peter Maydell
Subject: Re: [Qemu-devel] [RFC 2/7] fw_cfg dma interface
Date: Thu, 23 Jul 2015 14:35:05 +0100

On 23 July 2015 at 14:13, Laszlo Ersek <address@hidden> wrote:
> On 07/22/15 19:18, Kevin O'Connor wrote:
>> Another possibility would be to place the new fw_cfg dma register
>> address into a named fw_cfg "file" (eg, "fw_cfg_dma").  The firmware
>> could then use the existing select/data fw_cfg interface to check if
>> the new dma interface is available by scanning for that "fw_cfg_dma"
>> file.  This has the advantage of not requiring a new "magic address",
>> but has the disadvantage of a more complex probe.
> I like this one so much that I'm worried I'm missing some details. :)

This requires the device itself to know its own address, which
is in QEMU possible but ugly enough to be worth avoiding.

For ARM MMIO the obvious answer is "the new register should
just go next to the first one". Does x86 do something that
means we can't put it somewhere equally straightforward
or do discovery via whatever x86 uses for discovering MMIO?

-- PMM

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