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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Wed, 03 Feb 2016 09:44:35 +0100
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Subject: Re: [Qemu-devel] [PATCH v4] Add optionrom compatible with fw_cfg
 DMA version
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To: Laszlo Ersek <lersek@redhat.com>
Cc: Marc =?ISO-8859-1?Q?Mar=ED?= <marc.mari.barcelo@gmail.com>, "Gabriel L.
	Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, Kevin O'Connor <kevin@koconnor.net>, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Marc =?ISO-8859-1?Q?Mar=ED?= <markmb@redhat.com>

  Hi,

> I think the "dma_enabled" property is not exposed to the user.

It is: "-global fw_cfg.dma_enabled=3Doff" works (as in: doesn't throw an
error).  Has no effect through as it gets overridden later on.

> The default value of "dma_enabled" in both fw_cfg_io_properties and
> fw_cfg_mem_properties is irrelevant; the actual property value is always
> overwritten in fw_cfg_init_io_dma() and fw_cfg_init_mem_wide(), which
> all of the init paths go through.

And IMHO we should not do that, so setting the property actually has an
effect.

> I agree that DMA capability should be filtered with machine type.
> However, that distinction should not be made using the current
> "dma_enabled" properties (i.e., of "fw_cfg_io_properties" and
> "fw_cfg_mem_properties". Instead, it should be made in the
> board-specific callers of fw_cfg_init_(io_dma|mem_wide).

Why?

cheers,
  Gerd